Move comment and metric definitions out of the code

[adam-waldenberg]

Specifically, the following;

comment.__comment_begining__
comment.__comment_end__
comment.__comment__
comment.__comment_markers_must_be_at_begining__

metrics.__metric_eloc__
metrics.__metric_cc_tokens__

These could be defined externally in a configuration directory. It would separate the the definitions out from the logic in the code and would make it easier to add additional language support.