Implemented ability to exclude code from coverage.

[alvinteh]

To exclude/include code from BlanketJS coverage, users should incorporate the following comments prior to the desired lines respectively:

blanketjs:ignore true
blanketjs:ignore false

[rjrodger]

+1
this is very useful for the use-case where you have code that runs in Node.js and the browser, and have to muck about with module detection - some code paths will never execute in the browser, for example

[akshayrawat]

Any update on this feature?