apidocs: updated generated autodocs
Updated User Guide links to point to new location instead of Google Code wiki.
Fix handling recursive variable definition in variable table.

Resolves #1759.
ug2html.py: Removed functionality to copy tool docs since we don't have them anymore (#1754)
List DateTime library in User Guide.

This way DateTime library docs are included in User Guide distribution which fixes #1741.

Other related changes:
- Enhance time format docs a little.
- Update ug2html.py to automatically recompile library docs.
- Update lib2html.py to ease recompiling all docs programmatically.
Add generated docs to .gitignore
XML: Fix handling comments when using lxml (#1748)

Decided to simply strip comments when using lxml. The standard ET also
strips comments so the behavior is consistent.

If someone actually would need comments with lxml, we can consider
adding support for them. It would require `Parse XML` getting new
argument like `preserve_comments=False` and probably also some
keywords for actually doing something to comments.
DateTime: Fixed default timestamp millisecond rounding. Resolves #1764.
UG: Updated docs about supporting tools.

- No tools are distributed with RF anymore (fixes #1754).
- Removed un-maintained list of external tools in favor of link to
  robotframework.org.
New pattern matching keywords in Collections

For issue #1724
Merge pull request #1756 from guykisel/pattern_matching_new_kws

New pattern matching keywords in Collections
Changed remaining test case files under atest/robot to plain text format.

Also started to use .robot extension as suggested by #1766.
atests: Renamed test case and resource files under atest/robot to use '.robot' extension.

Renaming resource files obviously required updating also resource imports. See #1766.
atests: Renamed common resource files to use *.robot extension.

See #1766.
atest/genrunner.py: enforce using .robot extension (#1766)
oops, broke python/jython 2.5 support by introducing with w/o from __futere__ ...
atest: .txt -> .robot conversion: missed renamed resource in jython only test (#1766)
atests: Converting test data to use .robot extension (#1766)

Converted bunch of files on test data side to use .robot extension.
Mainly changed .txt to .robot, but also convered some affected HTML
files to plain text.

Plenty of boring work to do still, but also so much done that wanted
to commit and push changes.
atest: Renaming test data files to use .robot extension (#1766).

Another massive commit. Now all .txt have been converted to .robot
except for files that actually contain just text or that are test data
for testing .txt format. Remaining task is converting .html (and
possible .tsv) files to .robot (except obviously for files related to
testin .html/tsv).

This is quite a bit of work. Hopefully it will pay back later...