add sphinx compiler

[skitazaki]

I've added new compiler to build html documents based on Sphinx. Does it help you?

Example Guardfile is:

#!/usr/bin/env python
# -*- coding: utf-8 -*-

from livereload.task import Task
from livereload.compiler import sphinx

Task.add('*.rst', sphinx())

[lepture]

@skitazaki I think it is a little annoying to add every possible commands. How about:

Task.add('*.rst', shell('sphinx build ...'))

And then you can call every commands with the shell function.

[skitazaki]

@lepture Good idea to add shell function. Do you have any plan to implement it? otherwise, I will try it.
I guess shell can also replace some compilers such as rstc.

[lepture]

@skitazaki You can have a try. I'd like to review and merge.

[skitazaki]

I've created another changeset. Could you review it?
The usage is:

Task.add('*.txt', shell('sphinx-build ...'))
# or 
Task.add('*.txt', shell('make html'))

shell function can also accept input/output path arguments to support rstc feature, but that may be over engineering.

[lepture]

@skitazaki Maybe you could add some docs at docs/compiler.rst.

 else:
        return _compile.get_code

I will not use an else here, because you don't need it.

[skitazaki]

@lepture I've added some docs, and remove else statement. thank you for your review.

Though off topic, missing compilers such as LessCompiler exists in document. Are docs obsoleted?

[lepture]

@skitazaki They are obsoleted. They are replaced by CommandCompiler.

[lepture]

@skitazaki Thanks. I would be happy, if you can make the documentation right on LessCompiler etc...

[skitazaki]

@lepture thank you to merge. I will update documents on the another pull request.