Use '@template[:[target][:mode]]' syntax to mark that a file should NOT be opened for editing

[bbugyi200]

For example, cookie tempA:dirA/targA @tempB:targB:modeB tempC will:

• Create dirA if it does not already exist.
• Initialize dirA/targA using the tempA template.
• Initialize targB using the tempB template.
• Set the file mode of targB to modeB (using chmod).
• Initialize tempC using the same name for the template and target.
• Open ONLY dirA/targA and tempC (the target version) in an editor.

[bbugyi200]

Depends: #16