Refactored class lti to use @properties and setters
This way the setters update the rest of the properties accordingly,
as suggested by Ralf Gommers.
Added _update method to class lti to refactor repeated code
MAINT: runtests: enable executing scripts via --python and --shell
DOC: improvements to HACKING

Add a link to the most up-to-date version of the document, and make
build setup instructions more prominent.
Update realtransforms.py

The docstring for dst has errors for **type II**.  I've updated the docstring according to the information on the wikipedia DST page.  As far as I can tell, the description at wikipedia is accurate, and can be used for the docstring.
DOC: link to numpydoc via a git submodule
Merge pull request #2657 from pv/numpydoc

DOC: link to numpydoc via a git submodule
Merge pull request #2656 from arichar6/patch-1

Update realtransforms.py, to correct docstring for dst.
Typo: removed repeated docstring
Simplified _update signature
MAINT: typo fixes

* two consecutive words
* sentences not starting with capital letter
* two consecutive spaces
Merge pull request #2655 from Juanlu001/lti-attrs

Refactor of lti class to use @property and setters
Merge pull request #2661 from TomasTomecek/build-tools-doc-typo

MAINT: typo fixes in comments