local path link handling

[aaronjudd]

local path links are not working in many of our documents. We need to document/explain/fix this strategy to get all our local paths working.

The problem:

We're currently seeing failing links like:

https://docs.reactioncommerce.com/reaction-docs/development/configuration.md

a working version of this link is:

https://docs.reactioncommerce.com/reaction-docs/development/configuration

It seems to work when the last segment in the path matches the last segment of a docPath defined in redoc.json.

[machikoyasuda]

Another example of linking bugs:

https://github.com/reactioncommerce/reaction-docs/blob/master/developer/tutorial/introduction.md
's first link to the style guide fails, but https://github.com/reactioncommerce/reaction-docs/blob/master/developer/styleguide.md works. All the rest of the links without the .md appended fail as well, like here: https://github.com/reactioncommerce/reaction-docs/blob/master/developer/tutorial/introduction.md#how-do-i-change-the-layout