`.gitignore` should allow customized entries

[mweiden]

Need

• As a developer using fogg, I want to add custom entries to the .gitignore file, so I can keep my git repo clean and not have to surgically add files to git.

Approach

This could be implemented similar to how README.md templating is done in fogg by having a fogg-specific section where fogg writes out it's entries and allows the user to write their own outside of that section.

[ryanking]

@mweiden it seems there are 2 ways we can do this–

1. have fogg write .gitignore once (like we do with the READMEs). Down side is that if we ever improve something here it won't get applied.

2. add a new feature to fogg that allows us to manage part of a file, perhaps between 2 markers. You could then add more entries below that.

I am included toward #2 but am happy to hear alternatives.

[mweiden]

@ryanking I like option #2 as well. This is what I had in mind. Seems to work fine in the README.mds.