drop non-alpnanumeric chars from Canonical Name

[rolandwalker]

following up on #2659, further steps toward an algorithmic
derivation of Canonical Name from App Name.

Also add two rules about hyphens which are implied and already
followed by every Cask.

[rolandwalker]

Paging @vitorgalvao for your review/opinions.

Having completed renames to become consistent with #2659, this is my next proposed step in defining the Canonical Name: delete non-alphanumeric characters.

The source of this rule (as before) is that this seems to be the general behavior of existing Casks. Enforcing this change would mean changing two current Cask names: tune-instructor.rb and join-me.rb.

Background & goals:

• fully define the steps to derive a Cask name
• provide a script which automates the steps
• simplify CONTRIBUTING.md by referring users to the naming script
• integrate the naming script with brew cask create
• reduce chance of duplicate submissions

[rolandwalker]

Moving forward, as this only affects 2 Casks.