Feature: File filters

[j-ulrich]

Implements --exclude and --include filters to give more control over which files are included in the coverage calculation.

--include filters have precedence over --exclude and --prefix. So the approach to filter is:

• Use --prefix to define the project base directory.
• Use --exclude to exclude unwanted stuff. Typically, this would be used to filter out using rather broad patterns, e.g. filter out complete directory sub trees (e.g. ".*[\\\\/]test[\\\\/].*") or files by extension (e.g. ".*\\.dox$").
• If necessary, use --include to include specific files that would otherwise be excluded.

[coveralls]

Coverage increased (+0.9%) to 71.512% when pulling 99e4c4ad444b91362f42deaf6d1c6775f600b1f2 on j-ulrich:feature/file-filters into 6a5c6a92059eeab0e06413a56525570d93c9c0ff on psycofdj:master.

[psycofdj]

Thanks @j-ulrich, I'm releasing this on pypi right away