Implement chunkBy.
Implement binary predicate for chunkBy.
Move std.range.chunkBy to std.algorithm.groupBy.
Refactor to eliminate redundant call to r.empty.

.savePrev and .prev should be private.
Merge pull request #1453 from quickfur/chunkBy

Implement groupBy.
Mark all modules under std.c package deprecated
Use core modules instead of std.c.xxx modules