fix typos
rewrite to avoid "Regular Expressions is pretty deep subject"
Merge branch 'patch-4' of github.com:mroswell/back-end-web-development into mroswell-patch-4

Conflicts:
	01_command_line_git_ruby/ruby_basics.html
Merge branch 'gh-pages' of github.com:pjb3/back-end-web-development into gh-pages