Fixes scanning directories for .js files in Windows.

--meta-tags option can now accept either a path to file or directory.
And one can use the option multiple times to name several files
one-by-one.

More accurate, as it's not only Markdown. If one desires doing
Markdown-only, then he can include RDiscount by himself and do
whatever he wants.

Previously it was either builtin ones or user-define ones.
Now one can have a combination of the two.

Each meta-tag class is now responsible for rendering a block of all
meta-tags of same type, complete with title and everything.
The transform method has been replaced with to_html method that
converts array of meta-tag contents into output HTML. No more are
there @title and @hidden attributes.

When there's more than one file, pop up a menu with all files.

One can now write:

    @param {Object} [scope=this]

And the default value will be `this`.

Instead printing out a warning.

Avoid fatal crash - instead print out warning.

Previously the overflow rule was together with font-size:79.8%,
but that was only applied to Tablet examples.

Wrap all icons in index pages inside div. For touch examples, add
extra touch-examples-ui class to examples index page and adjust the
styling a little in CSS.

Modified origin commit by Nick Poulden by wrapping ExtJS welcome
page inside <div id="extjs-welcome"> similarly to Touch welcome
page inside <div id="touch-welcome">.  This way they're both
nicely wrapped and ExtJS welcome page doesn't get screwed up.

Previously we relied on builtin maxHeight of container, but that
also limited the height of the live preview which we wanted to be
larger.  Not doing our own bounds-checking.

The happened when the welcome page was first loaded and then one
switched to API tab. It happened because the class tree was activated
while it was hidden, so height calculations couldn't be performed
correctly. Fixed by adding an empty item to trees container that's
activated first instead of the class tree.