Remove unused module `Util.Tar`

This was apparently a never-completed internal tarball extraction
implementation. In reality, hsenv just shells out to the system's `tar`
binary.
Formatting
Clarify the hsenv directory name in the usage message
Don't auto-wrap the usage message "outro"

This screws up explicit formatting.
Add a usage blurb about activating and deactivating the sandbox

Closes #35
Tentative doc update
Fixed char stripping of md files
updated README to support code correctly
Final commit before first PR
Various minor tweaks to README content on top of adinapoli's work
Shell snippet formatting

Adds syntax highlighting (via GitHub Markdown or Pandoc) and removes the
unnecessary leading `>`s in code blocks.
Documentation modernization and cleanup

Merge branch 'updated-docs'
Pre- and post-activation hooks.

The activate and deactivate scripts will call
~/.hsenv/bin/(pre|post)-(de|)activate at the appropriate times.
Merge remote-tracking branch 'upstream/master'