Make latex run 3 times by default.

Needed to get all the resulting PDF cross-references right.
Change rendering of '=>', chapter 3 updates.

Added a definition \resultingin that typesets the => (\Rightarrow) with a bit more space to make it obvious separate from either side.  Various updates to chapter 3 (data types) to tidy up typesetting;  also changed/added the odd sentence here and there to clarify and/or improve readability.