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
