OCS Manual: Fixed LaTeX compile

excess end{} statement
OCS Manual: Start of Referenceables table

The beginnings of the referenceables table (WIP) Also, added several
commands - these should probably be moved to a global command file if
possible
OCS Manual: Customisations

Added xcolor package for \colorbox{} support
Adjusted paper/margins to get more width on page
OCS Manual: Added file type to gitignore

TexLive generates a main.synctex.gz file on compile. Filter it out of
commits (if I have the terminology right!)