Project introducing stdout/stderr and error handling (#116)

There is a lot of "teaching" material in this project, and I'd love to
cite some external references rather than writing new material, but I
couldn't find any particularly accessible (and
not-very-language-specific) introductions to the concepts...

Co-authored-by: Sally McGrath <[email protected]>

prep/README.md

@@ -80,7 +80,7 @@ It doesn't matter what this does: what's important is the input command and the
 Input command:
 
 ```console
-curl -i 'http://localhost:8080/'
+> curl -i 'http://localhost:8080/'
 ```
 
 Expected output:

projects/README.md

@@ -18,6 +18,8 @@ Each project has its own directory with a README.md file that has instructions.
 
 Most exercises finish with a list of optional extension tasks. It's highly recommended that you try them out. Note that often the extensions are open-ended and under-specified - make sure to think about them with a curious mind: Why are they useful? What trade-offs do they have?
 
+1. [Output and Error Handling](./output-and-error-handling)
+   <br>An introduction to how to handle errors in Go, and how to present information to users of programs run on the command line.
 1. [CLI & Files](./cli-files)
    <br>An introduction to building things with Go by replicating the unix tools `cat` and `ls`.
 1. [File Parsing](./file-parsing)

projects/file-parsing/README.md

@@ -55,7 +55,7 @@ The format is as follows:
 The tool `od` (which you can learn more about [here](https://man7.org/linux/man-pages/man1/od.1.html)) can be useful for exploring binary data. For instance, we can run:
 
 ```console
-% od -t x1 projects/file-parsing/examples/custom-binary-le.bin
+> od -t x1 projects/file-parsing/examples/custom-binary-le.bin
 0000000    ff  fe  0a  00  00  00  41  79  61  00  1e  00  00  00  50  72
 0000020    69  73  68  61  00  ff  ff  ff  ff  43  68  61  72  6c  69  65
 0000040    00  19  00  00  00  4d  61  72  67  6f  74  00                
@@ -99,21 +99,21 @@ Two examples of this are [`jq`](https://stedolan.github.io/jq/) (which allows yo
 For example, you can use `jq` to answer the question "Who had the highest score" without needing to write a whole program:
 
 ```console
-% jq -r '. | max_by(.high_score).name' file-parsing/examples/json.txt
+> jq -r '. | max_by(.high_score).name' file-parsing/examples/json.txt
 Prisha
 ```
 
 Or use `fx` to do the same, but using more familiar JavaScript as the query language:
 
 ```console
-% fx file-parsing/examples/json.txt '.sort((l, r) => r.high_score - l.high_score)[0].name'
+> fx file-parsing/examples/json.txt '.sort((l, r) => r.high_score - l.high_score)[0].name'
 Prisha
 ```
 
 Similarly, a program called [`csvq`](https://github.com/mithrandie/csvq) can be used to query CSV files in a SQL-like query language:
 
 ```console
-# cat examples/data.csv | csvq 'SELECT * ORDER BY `high score` DESC LIMIT 1'
+> cat examples/data.csv | csvq 'SELECT * ORDER BY `high score` DESC LIMIT 1'
 +--------+------------+
 |  name  | high score |
 +--------+------------+

projects/metadata.json

@@ -1,6 +1,8 @@
 {
   "order": [
+    "output-and-error-handling",
     "cli-files",
+    "file-parsing",
     "http-auth",
     "server-database",
     "multiple-servers",

projects/multiple-servers/README.md

@@ -78,7 +78,7 @@ There's a good, short guide to workloads on [scaleyourapp.com](https://scaleyour
 
 Our file layout for this project will look like this:
 
-```console
+```
 api/
     api.go
 assets/
@@ -108,12 +108,14 @@ Specifically, the `cmd/` files will import functionality from `api` and `static`
 
 In reality, starting each will look like this:
 
+API server:
 ```console
-# api server
-$ DATABASE_URL='postgres://localhost:5432/go-server-database' go run ./cmd/api-server --port 8081
+> DATABASE_URL='postgres://localhost:5432/go-server-database' go run ./cmd/api-server --port 8081
+```
 
-# static server
-$ go run ./cmd/static-server --path assets --port 8082
+Static server:
+```console
+> go run ./cmd/static-server --path assets --port 8082
 ```
 
 > 💡 See the [prep README.md](../prep/README.md#command-line-examples) for an explanation of this command line example.
@@ -328,7 +330,7 @@ import (
 The rest is up to you: hook this together and make this work:
 
 ```console
-$ go run ./cmd/static-server
+> go run ./cmd/static-server
 Hello!
 ```
 
@@ -339,14 +341,14 @@ To do that, add support for a command like flag: `--path` which will be where th
 Make this work:
 
 ```console
-$ go run ./cmd/static-server --path assets
+> go run ./cmd/static-server --path assets
 path: assets
 ```
 
 We also want this server to run on a specific port. Make this work:
 
 ```console
-$ go run ./cmd/static-server --path assets --port 8082
+> go run ./cmd/static-server --path assets --port 8082
 path: assets
 port: 8082
 ```
@@ -364,7 +366,7 @@ It's possible to do this all in <20 lines of code.
 At the end, you should be able to run the server and visit [http://localhost:8082](http://localhost:8082) to see the image gallery!
 
 ```console
-$ go run ./cmd/static-server --path assets --port 8082
+> go run ./cmd/static-server --path assets --port 8082
 ```
 
 We aren't loading the list of images from an API yet; they're hard coded in the JavaScript. Making the API work is coming next.