cleaned up doc directory; got rid of nrel docuemnt files; added latex files to .gitignore
cleaned up doc directory; got rid of nrel docuemnt files; added latex files to .gitignore


Former-commit-id: 058d0b06e7c3990c6023fc0369d5a1434a459952
OpenFAST/OpenFAST,OpenFAST/OpenFAST,OpenFAST/OpenFAST