Remove require rubygems from source code.

Removed from anything that is wrapped by gem when installed by gem.
Fixes #338.
Symlink extjs-build & touch-build dirs in dev-mode.

Just to speed up creating these builds.
Add "Open in new window" button to ExtJS examples.

Simply copy over the toolbar code from Touch example component
and generalize the handler for the button.
Align "Open in new window" button to right.

Looks better IMHO.

In the case of Touch examples, the separator is no more needed
in this case.
Automatically read config from jsduck.json file.

Check if jsduck.json exists in current working dir, if yes, then
read configuration from it.

Fixes: #335
Switch again back to using ExecJS middle-layer.

This is to allow third-party packaging of JSDuck without the
inconvenient dependency on therubyracer gem.

Fixes: #339
Add {DATE} and {JSDUCK} placeholders to --footer.

To easily insert current data and link to JSDuck homepage.

Fixes: #343
Add execjs dependency to .travis.yml.
Typo in command line option docs.
Up version to 4.7.0.
guides: Add <h3> to TOC