Escaping '*' for consistent markdown highlighting

Using *BSD highlighted the remaining text as bold inside vim.  Escaping the
'*' removes this issue and works in standard and GitHub markdown.
Consistently capitalising 'Perl'

The word 'Perl' was used both capitalised and lowercase versions often
referring directly to the same thing.  This change at least makes the usage
consistent.  I could make all instances lowercase if that is the preferred
usage.
Correcting plural usage
Consistently hiphenating "pull request"
Minor grammatical corrections to GitGuide text
Consistently capitalising "perlbrew"
Formatting "dzil" as code in running text
reflect changes
Merge branch 'pr/git_guide_markdown_fixes'