DOC: Fix formatting.
DOC: Fix broken links.
DOC: Make sure release placeholders is short version
DOC: Remove redundant and outdated information.
DOC: Add FAQ page
Merge pull request #1527 from jseabold/update-docs

DOCS: Update docs add FAQ page
DOC: Fix link
Merge pull request #1530 from jseabold/fix-link

DOC: Fix link
DOC: Fix link.
DOC: Ran linkcheck. Fixed links.
Merge pull request #1531 from jseabold/fix-links

DOC: Fix stale links with linkcheck
DOC: Fix link to code on github
Merge pull request #1533 from jseabold/fix-gh-links

DOC: Fix link to code on github
ENH: Unit Root Tests

Introduces 4 new unit root tests and provides a class for Augmented Dickey Fuller testing.
The four new tests are:
  - PhillipsPerron
  - KPSS
  - Variance Ratio
  - DF-GLS

These have all been included in unitroot.py, and the afduller function has been moved from
tsatools to unitroot, and is now just a wrapper around the ADF class.

The critical value and p-value lookup codes have also been consolidated into untiroot.py.
Critical value and p-value lookup information for DFGLS and KPSS is not readily available
in published form, and so simulations were performed to generate these using 100,000,000
replications using a methodology similar to MacKinnon (2010).  All critical value data
has been consolidated into tsa/critical_values.

A cov_nw function was added to tsa/stattools which computes Newey-West covariance.

Also includes substantial improvements to tsatools, including numerous bug fixes.   The
code that handled recarrays has been improved to now handle pandas dataframes.  Numerous
doc strings where improved.  Test coverage was also substantially increased.

string_types was added to the compatibility library to address the difference between basestring
in Python 2 and str in Python 3.

Moved coint to a new file coinegration.py which will, in the long term, be expanded to include
other tests for cointegration.
Changed h0 and hA to null_hypothesis and alternative_hypothesis

Provides a __str__ and __repr__, as well as a _repr_html_ for IPython, for unit
root tests to improve interactive behavior

Refactored valid_trends to remove redundant code