spec: use macrocache to store total test count (#56)

nimskull does not allow compileTime variable to be reached from
potentially runtime code.

While this issue could be solved by adding compileTime to totalTests,
doing so breaks the variable due to
nim-works/nimskull#1022.

Instead, store the counter using macrocache, which avoids this issue
rather nicely (and is the recommended way in Nim to store these values).

balls/spec.nim

@@ -1,5 +1,6 @@
 import std/times
 import std/macros
+import std/macrocache
 import std/os
 
 import grok
@@ -120,11 +121,11 @@ type
     clock*: float          ## used to measure test timing
     memory*: int           ## used to measure test memory
 
-var testCount {.compileTime.}: int                       # whatfer counting!
+const testCount = CacheCounter"balls.spec.testCount"     # whatfer counting!
 
 proc totalTests*(): int =
   ## reveal the value of the counter without exposing it
-  testCount
+  testCount.value
 
 proc init*(test: var Test; name: string; code: NimNode) =
   ## initialize a test with the most basic input possible
@@ -133,7 +134,7 @@ proc init*(test: var Test; name: string; code: NimNode) =
   test.node = nnkStmtList.newNimNode(code)
 
   inc testCount
-  test.number = testCount
+  test.number = testCount.value
 
   # we've stored the original code in the Test object, so now we
   # copy the input and put it into a new statement list; `node` will
@@ -149,7 +150,7 @@ proc init*(test: var Test; name: string; code: NimNode) =
     # the test number so as not to make the user think we skipped some
     # tests
     test.number = 0        # set the test number to zero as a sentinel
-    dec testCount
+    inc testCount, -1
 
 proc dollar*(n: NimNode): NimNode =
   ## If it's not a string literal, dollar it.