Updated build API for 1.4.0

[rabitt]

Implements option B from issue #106

• build_file takes array or file inputs and generates file outputs, returning a boolean
• build_array takes array or file inputs and returns np.ndarray outputs

build_file is an alias for build, and I moved the documentation to point people towards using build_file, while keeping build fully functional.

I also did a little cleanup of how set_input_format and set_output_format work - rather than storing the list of format arguments to be passed to sox, it stores a dictionary which is parsed when running build/build_array, which cleans up the build functions substantially.

[rabitt]

cc @pseeth @nicolamontecchio @psobot @carlthome @hadware @lostanlen @justinsalamon

[coveralls]

Coverage increased (+0.4%) to 99.104% when pulling 5830789 on build-api into 0591cb8 on master.

[pseeth]

Awesome work! Seems coverage is falling a tiny bit but other than that, lgtm!

[pseeth]

Any chance of a merge into master and a pip release if this is ready?

[rabitt]

@pseeth this is up on pypi! pip install pysox --pre
give it a spin and let me know if you run into any issues

[carlthome]

Nice!