ENH: moment_helpers, cov2corr add option, new corr2cov
ENH: nearest positive definite correlation and covariance matrix, first version
BUG/TST fix nearest_cov, add tests against R
REF: rename corr_xxx, postfix adjective
REF move correlation_tools to statsmodels.stats
DOC add new functions to api and stats.rst
DOC: improve docstrings (Vincent's review), moment_helpers docstring
Merge pull request #631 from josef-pkt/correlation-psd

Correlation positive semi definite #303