implements {.compile.}

[ringabout]

fixes #357

ref https://github.com/microsoft/mimalloc

• Make hastur download mimalloc as part of the build process. Maybe depend on it via a git submodule.
• Add .compile: "foo.c" to Nimony so that we can also depend on C code like mimalloc.
• Make use of .compile in system.nim so we can use a decent memory allocator which offers allocatedSize() so that our new super efficient strings and seq can use it.

[ringabout]

{.compile.} is almost finished, but it requires

• importc mangling support
• currentSourcePath: so {.compile("$path", "-I$includedPath").} can get the source path for parameters at the compile time
• semcheck for compile and handle path better exactly like the Nim compiler

[Araq]

Have you considered to make Nimony emit (compile "foobar.c") information to the generated index file. Then it would be precise for when x: {.compile ...} and it would not require this ugly Nifler addition. The dependency analyser might have trouble with that though... :-(

[SirOlaf]

Suggested change

	{.compile("foo.c", "-fno-strict-aliasing")
	{.compile("foo1.c", "-fno-strict-aliasing").}

[ringabout]

done

[ringabout]

Succeeded by #383