(CFACT-88) Replace string utility functions with those in Boost.

Replacing the following string utility functions with Boost string
algorithms:

* starts_with
* ends_with
* ltrim
* rtrim
* trim
* tokenize
* split
* to_lower
* to_upper

Also removing the unused ci_string type.  Boost has functionality for
doing case insensitive comparisons.
Merge pull request #109 from peterhuene/maint/strings

(CFACT-88) Replace string utility functions with those in Boost.