* Added `regex` match_type as valid config callout in both individual mappers
and mapper defaults
* Added test coverage for changes
* Updated documentation to reflect usage of `match_type` parameter and
provide example of a raw regex match rule
* Removed legacy mapper config parser
* Removed logic to switch to YAML parsing based on mapping filename
* Removed tests for legacy mapper config
* Remove references to legacy mapper config format from `README.md`
* When a terminating newline is missing from the metric mapping configuration file, the last definition is not parsed at all. After this change the last 'METRIC_DEFINITION' in the file is equivalent to a newline (either between definitions or as the terminating newline).
* Update mapping, if we are reading the last line of the file. Otherwise we will append the mapping and lose the last label. Since we are updating the mapping in two different places a 'updateMapping' function was introduced.
* Added mapper test for config files without a terminating newline.
* Added another test case where multiple definitions are given without a final terminating newline.
* As suggested by @grobie, we should give an error when a terminating newline is missing. Updated tests accordingly.
