Build script bug and updating dependency constraints.

[jship]

* Update project to be compatible with stack using LTS snapshot 3.18.
* Add gitignore file that is aware of both stack- and cabal-based binaries/intermediate files.

• Fixed issue with non-existent Hierarchy.png image trying to be copied in the build script.
• Relaxed doctest and filepath dependency constraints.
• Bumped min version of numeric-qq to 0.1.3.
• Set range of acceptable versions of base.

[jship]

Travis check failed due to dependencies. Will update the Travis config to use stack later today.

Based on comments from a pull request I put in on numeric-qq, following the same requirements on this PR. Not using stack, but making sure stack will work out-of-the-box with LTS-3.18.

[jship]

Thought Travis was failing due to dependencies but it was actually from the customized Setup.hs build script. This script was trying to copy a non-existent 'Hierarchy.png' file into the Haddock output directory. This custom setup code was based on a version of @ekmett's lens library.

Removed call to copyFiles from Setup.hs as a hierarchy image is not distributed in the repo.

Travis is passing now using stack's LTS-2, LTS-3, and the latest nightly snapshot. This covers GHC 7.8.4, 7.10.2, and 7.10.3.

[jship]

Closing this pull request as the changes are captured in my latest PR: #2