Copy variable parameters into a message buffer rather than just storing pointers
Bug fixes
Write to a heap buffer (in case there are lots of Events/Markers on the stack)
Add UT infrastructure
Use STL strings instead of byte arrays to build parameters
Code tidy
No need for _params_buffer to be protected
Switch to storing variable len params as separate strings rather than in a single buffer
Add an accidentally deleted add_var_param function
Fix compiler warnings
Inline to_byte utility function
Move test utils to ut folder
Remove some unesessary variables, and add a couple of comments
Merge pull request #27 from Metaswitch/issue23

[Reviewer: Mike][From: Alex] Copy variable parameters into internal memory