Add documentation build step to Travis CI script.
Add documentation build step to Travis CI script.

Fixes #163.

bladams/pymssql,ramiro/pymssql,pymssql/pymssql,JimDennis/pymssql,pymssql/pymssql,bladams/pymssql,bladams/pymssql,JimDennis/pymssql,zerolugithub/pymssql,klothe/pymssql,ramiro/pymssql,klothe/pymssql,zerolugithub/pymssql,zerolugithub/pymssql,JimDennis/pymssql,klothe/pymssql,ramiro/pymssql,Aloomaio/pymssql,Aloomaio/pymssql,Aloomaio/pymssql