Get rid of :property_like and :member_like categories.

Only use the :method category in @merge_context.

So no more does one need to choose between two types when creating
his own member type.

The only problem at the moment is that I needed to add explicit check
for :cfg/:property/:css_var to Tag::Type#merge.
Upgrade prettify lib to 4 Mar 2013 version.

This contains a fix for the changed newline handling in IE10.

Fixes: #373
Up version to 4.10.1
Merge branch 'master' into doc-tags
Move merging of :type field to Cfg/Property/CssVar classes.

A bit of a duplicated code in Cfg and Property, but we get rid of
the explicit check for :cfg/:property/:css_var in Type class.
Extract :params field merging to separate class.
Move :params field merging to Method & Event classes.
Move all class-level merging to Tag::Class.

With this we completely get rid of the @merge_context variable,
and all the merging happens in Tag::Class or MemberTag subclasses.
Document why we have a static method in Merger class.

Plus a typo.