Corrected the theilslopes implementation and added a test
Moved implementation to `stats.theilslopes`. Added tests to `stats`.
Added y ties term to the confidence interval calculation.
PEP8 fixes
MAINT: minor cleanups to stats.theilslopes.

Add complete references, reST formatting, PEP8, etc.
DOC: add example for stats.theilslopes.
DOC: remove docstring of stats.mstats.theilslopes, use stats version.
DOC: added notes about example for stats.theilslopes. Changed example wording.
Minor changes to docs for stats.theilslopes
Merge pull request #3574 from tomflannaghan/theilslopes-fix

Fixes multiple bugs in mstats.theilslopes