Language tagging about code-prettify HOT 5 CLOSED

Language tags should be easy to recognize and remember.

Since we use class="prettyprint" to identify regions to prettyprint, I suggest 
the
following convention

class="prettyprint"  -- make a best guess as to language
class="prettyprint lang-java"  -- do java prettyprinting

The "lang-" prefix is followed by the filename extension commonly used for 
source
files in that language to avoid problems with C# not being a valid html 
identifier. 
We will use cc for C++ since it is an identifier, and more commonly used than 
cpp or cxx.

To flesh out the high level design, the prettify loop will be changed to:
(1) Extract tags and store [tag, position-in-string]
(2) Use a regex based lexer to lex the string sans tags
(3) Run a classifier over tokens
(4) Merge tags back into token list and join tokens to produce html
from the current
(1) Split into chunks of tags | text
(2) Split text chunks into tokens using a state machine over a character 
iterator
that unescapes entities lazily
(3) Join token list to produce html



This will cut out the hand coded state machines that iterate over characters,
replacing them with the regex based lexers from 2.

We can then define a language handler as a { lexer, classifier } pair.

Define a language handler for C-style langs and one for markup langs to get us
backwards compatible.

Modify the main prettify function to look for a lang-\w+ class, and, if present,
choose the appropriate lexer.

Implement a lisp/scheme lexer to demonstrate that new handlers can be added and 
document.

Implement other lexers as demanded.

Finished rewriting the existing lexers to use PR_createSimpleLexer which is 
regexp based.

I realize this would be an entirely different thing, but what about taking 
advantage
of a library of pre-written syntax highlighting rules, like VIM's? The
syntax-defining commands aren't that complicated. (Well, they don't seem to be, 
what
do I know?)

@r38