Include legacy documentation in pdf and MS Word format - General & ElastoDyn

[rafmudaf]

Feature or improvement description
Until the legacy documentation can be fully converted to the readthedocs / sphinx format, we will be including old documentation in the existing format.

This pull request included documentation general to OpenFAST, as well as documentation on mesh mapping and linearization.

Related issue, if one exists
#804

Impacted areas of the software
Online docs.

Test results, if applicable
See the documentation live at https://raf-openfast.readthedocs.io/en/docs-legacy_docs/source/user/index.html

[andrew-platt]

Good idea. This will work for now.

Should we add a note that the legacy documentation may be out of date?

[rafmudaf]

@andrew-platt good point, I've made that note.

[rafmudaf]

@jjonkman This pull request is ready for review. I've changed the name to reflect that it covers general OpenFAST documentation and ElastoDyn. I will create another pull request to do the same for the module-specific documentation.

[jjonkman]

Thanks, @rafmudaf. Very nice to see these documents being added to the OpenFAST documentation as a stop-gap measure! Please find my edits and comments below.

[jjonkman]

Thanks for addressing my edits and comments. I approve now.