Fix front matter for 'Creating a New Theme'

There seems to be an issue with TOML and certain menu structures. Current workaround: YAML.
Add an `install` target to Makefile.
Add timezone to buildDate
Fix various Windows-issues

File handling was broken on Windows. This commit contains a revision of the path handling with separation of file paths and urls where needed.

There may be remaining issues and there may be better ways to do this, but it is easier to start that refactoring job with a set of passing tests.

Fixes #687
Fixes #660
Added top level .Hugo variable with version, commit and generator information
Added Version, CommitHash and BuildDate to hugolib/hugo.go and used it in build
Removed commitHash and buildDate from commands/version.go and used hugolib vars
Removed getDateFormat function from commands/version.go