* add ability to add assembly files when building an exe, obj, or lib
* add implicit cast from `[N]T` to `?[]const T` (closes#343)
* remove link_exe and link_lib in favor of allowing build_exe and
build_lib support no root zig source file
See #329
Supporting work:
* move std.cstr.Buffer0 to std.buffer.Buffer
* add build.zig to example/shared_library/ and add an automated test
for it
* add std.list.List.resizeDown
* improve std.os.makePath
- no longer recursive
- takes into account . and ..
* add std.os.path.isAbsolute
* add std.os.path.resolve
* reimplement std.os.path.dirname
- no longer requires an allocator
- handles edge cases correctly
* add std.os.deleteTree
* add std.os.deleteDir
* add std.os.page_size
* add std.os API for iterating over directories
* refactor duplication in build.zig
* update documentation on how to run tests
