base/*_util* -> util/

We had effectively built a namespace within base for things which are just adding more functions to standard objects.

Things like:
 - <base/stl_utils> which adds helper functions for members we wish the STL had
 - <base/string_utils>: Make cstrings more accessible
 - <base/io_utils>: Make reading/writing to fds easier

Things like:
 - <base/fd>: Change linux fds to be RAII don't apply because they're more than just little helper functions that take standardized things
Merge pull request #111 from cmaloney/util-updates

base/*_util* -> util/