[tidy] Major clean-up 2014Q1 -

* Increment year in the copyright headers
* Add missing copyright headers
* Undoxygenize the code, leaving only important comments
* Add one missing `#ifdef __cplusplus`
* Remove one unused struct defenition
* Fix guard macros in some headers to reflect on file name changes
* Remove blank lines in various places
Merge pull request #90 from xively/undoc

[tidy] Major clean-up (2014Q1)