Merge pull request #95 from dominics/documentation

[doc] Start documenting Predis.

This PR takes care of the initial Sphinx structure and focuses on clustering as the first theme.
[doc] Describe available connection parameters.
Merge pull request #96 from nrk/doc-connection-parameters

[doc] Describe available connection parameters.
[doc] Describe available client options.
[doc] Add missing description for "password".
[doc] Fix code snippet used for client options.
[doc] Added Lua scripting documentation.
Merge pull request #99 from ronnylt/doc-lua-scripting

Lua scripting documentation.
[doc] Add note about client options values returned by callables.

Predis will not attempt to use its standard configuration path for
options when using callables as initializers, this makes sense and
it is an intended behavior to give users more flexibility over the
configuration of the client but it can be confusing and unexpected
in certain cases such as with the combination of server profile and
key prefix.
Merge pull request #97 from nrk/doc-client-options

[doc] Describe available client options.