Updated the user guide.

Mostly re Job Polling, plus some typo corrections etc.
More minor User Guide changes.

Correcte some typos, added to a style guide section; added to the cylc history
section.
Minor CUG timezone text update.
More minor CUG text updates.
Add tests: log/job/ and work/ in selected cyclers
Merge pull request #1083 from matthewrmshin/t-cyclers-dir-struct

Add tests: log/job/ and work/ in selected cyclers
Updated the Tutorial for new log locations etc.
Improved vim syntax file.
Merge pull request #1081 from hjoliver/cug-update

Updated the user guide.
Use standard vim syntax groups.
Merge pull request #1085 from hjoliver/vim-syntax-update

Improved vim syntax file.