fix some typos
delete trailing whitespaces
Add consitency by using Verb (infinitive uppercased) and not
verbs (conjugated lowercased).
fix with @code{} when needed
Fix Gnuplot and GnuCash syntax accodingly first page of web site.
Fix url
fix emphasis
fix double quotes
suppress double spaces before ':' and ','
Merge pull request #180 from thdox/documentation-typos

Documentation typos