Remove Fog.class_from_string

This was a helper for the VSphere provider that was attached to the
global Fog module.

It was not used anywhere else so does not warrant begin maintained as
part of core.

It is dealt with in fog in https://github.com/fog/fog/pull/2787
Lock rake to 10.1 for Ruby 1.8.7

Rake has gone 1.9.3+ from 10.2 onwards so the Gemfile for 1.8.7
specifies this new constraint.
Merge pull request #31 from fog/fix_rake_on_187

Lock rake to 10.1 for Ruby 1.8.7
Merge pull request #29 from fog/remove_class_from_string_helper

Remove Fog.class_from_string
Fix some typos in spec descriptions
Cleanup some documentation and tags
Test and document the existing Fog::Service class
Extract setting cleaning code to utility class

`Fog.symbolize_credentials` is actually a `Hash.symbolize_keys`
implementation with an exception for Headers.

Whilst it appears to be related to credentials (which is an assortment
of class methods around a Hash not an class) it is only used by
Fog::Service.

This extracts it as a start of a shared utility class whilst various
bits of randomness are pulled to sensible places.
Refactor code to handle service options
Break down setup_requirements to smaller parts

Note that a number of providers require each model when collections are
declared so the `require_models` step was almost redundant due to that
approach being used throughout fog.
Extract extra long version of CamelCase

This had been using Array/Range magic to do String#capitalize and
joining with the default argument.
Update specs to use asserts

Core team have decided to use asserts rather than must expecations
within minitest/specs.
Merge pull request #32 from fog/cleanup_service_settings

Cleanup Fog::Service settings
Passing specs for existing behavior
Initial removal of Rackspace specific conditional
Moved provider assertion earlier allowing removal of explicit return
Oops! Looks like Rackspace scopes the file correctly in the library
but differently in the module namespacing.