The loading of all meta-tags at the start of several test-suites
slowed things down quite a bit.  Now only loading support for
@static in most places and only loading the full set of meta-tags
in one suite that tests all of them.

Also moving @markdown tag test to be together with other meta-tag tests.

Got the running time of tests down from 1.18 to 0.85 seconds.
That's about 1/4 faster. Not much, but it's a good goal to keep
the running time under a second.

Also document why it does things the way it does.

When #foo is found inside text, it is automatically interpreted
as {@link #foo} when the current class happens to have a member
called #foo.

Previous implementation was very hackish. Now only doing auto-detection
when not inside HTML tag (i.e. between <...>) and when not already
inside HTML link (i.e. between <a>...</a>).

As a result the #replace_class_names method is quite a bit simpler, as
it can be sure that it's always executed in valid context.

Previoulsy they were white on white, which was a horrible default.

Previously the list was hard-coded. Now all meta-tags with signature
defined are automatically included, and the order is the alphabetical
order of filenames (for builtin tags).

MetaTagLoader now only deals with loading and has no other knowledge
of builtin tags than the path ./tag from which it loads when :builtins
is passed to #load method.

The loader is now only accessed through MetaTagRegistry#load and not
directly any more.  This simplifies the tests a little bit - they now
only have to do one simple call to MetaTagRegistry.instance.load.

One can now write: @cfg foo-bar

Further more, the DocParser no more differenciates between CSS and JS
identifiers, using the same pattern for both.

A regression cause by implementing @deprecated as meta-tag but
forgetting to set the formatter context before calling #to_html.

Previously @inheritdoc only looked for member with same name from
parent class, now we also look from mixins.

This avoids code like: tag.key || tag.name

Also the :meta hash now always contains symbol indexes, not mix of
strings and symbols.

This way the hash of tagname->tag is built in one place just once.
Also no need to pass around the meta_tags array to every object
that happens to deal with meta-tags.

The list of signature attributes is also produced by this registry.

Each attribute is now defined in separate file as meta tag.

Previously some settings were directly on Docs object, others in
Docs.data - a bit messy.

At the moment only treating file as JSB if it has .jsb3 extension.
I'm not sure if the format of .jsb2 or whatever might be different,
so better be safe than sorry.

At the moment this is a bit of a hidden feature, but it could be
explained in manual.

Also convert paths to canonical format.

List of attributes to show in signature is now kept in Class and
used by both front- and backend.

New warning type 'no_doc' - shown when class or member has no
documentation at all.

One can now use {@link #static-foo} to link to static member #foo
in case there's instance member with the same name. This wasn't
previously possible.

Instead of adding two different sets of keys to one hash, build the
hash just by member name.  Look member name up from hash and filter
by type if needed.

Doing things in this more correct way brought up some bugs in other
places. Like {@link #foo-bar} being detected as link to member foo
of type bar, which happened to work. Now we only detect correct types.

Similarly the @inheritdoc happened to work because string interpolation
handles both symbols and strings equally well. Now it needs to be
converted to symbol explicitly.

All-in-all we now have more correct implementation.

Also turn off -link_ambiguous for Touch2.

Like when {@link #foo} refers to either #method-foo or #event-foo.

Also add new warning type: link_ambiguous.

-link now only hides warnings about links to non-existant items.

-link_private hides warnings about links to private members.

Default values make sense for properties too.  Previously I thought
that they don't but people are already using them, so here we go...