Add more user-friendly checks for output file compression options

 * No longer assert fail if the level is outside the allowed range
 * Actually check that a valid compression method has been provided
 * Failing either check will result in NULL being returned by
   trace_open_file_out and the libtrace error being set appropriately
 * Added TRACE_OPTION_COMPRESSTYPE_LAST to compression method enum, so
   we can always easily tell if the value is outside the expected range.
Merge branch 'nicercompressionoptions' into develop