Added outline for section on creating custom frame mojit.
Created draft of section on creating custom frame mojit.
Fixed a formatting issue with the reST.
More fixes to the reST.
Made edits.
Linked to the master version of 'HTMLFrameMojit' and added an explanation of the advantages of your frame mojit having a 'child' instance.
Merge pull request #964 from zhouyaoji/docs_create_frame_mojit

[doc] Added a section in the Frame Mojit chapter explaining how to create custom frame mojits.