README fixes
README.rst mention submodule existence
Merge pull request #217 from gberaudo/readme

Some fixes in Readme
Add optional tiles_url for apache config and s3 cache
Code style
Merge pull request #218 from sbrunner/base_url

Add optional tiles_url for apache config and s3 cache
Add 'Configure Apache' documentation.

With the new tiles_url cache option.
Add partial server support