zig build system improvements, add some std API

* add std.buf_map.BufMap
 * add std.buf_set.BufSet
 * add std.mem.split
 * zig build system improvements (See #204)
   - automatically parses NIX_CFLAGS_COMPILE and NIX_LDFLAGS
   - add builder.addCIncludePath
   - add builder.addRPath
   - add builder.addLibPath
   - add exe.linkLibrary
1c6000d047Andrew Kelley committed on 4/4/2017, 5:52:20 AMparent72fb244
9 files changedLine totals unavailable