Win32 support for RDiscount & removing Maruku

[BPScott]

Currently Windows support is provided by using Maruku instead of Rdiscount if the ruby platform is detected as windows. This is because Rdiscount is a native gem and needs to be compiled, which ruby on windows does not provide the tools for out of the box.

This is not immediately obvious to users and if Toto is installed using gem install toto, toto shall fail to run as Maruku is not defined as a dependency. To get this dependency working a user must checkout the source, and regenerate the .gemspec file or run gem install maruku. This functionality is not documented.

Fortunately it is now possible to build native gems on windows using the Windows Devkit so I propose that:

1. The commit that added this functionality is reverted, so Toto no longer attempts to fall back to Maruku
2. A section is added to the readme stating that Toto is dependant upon rdiscount, which on windows must be built using the devkit and instructions on how to do so can be found at https://github.com/oneclick/rubyinstaller/wiki/development-kit