Add new JavaScript writing methods

Added writeVariable methods
Added writeComment method
Added endStatement method
Added functionCallBlock methods
Added functionCall methods
Added more constants to JavaScriptWriter

Made BackboneModelProcessor use new JavaScriptWriter methods
New methods makes writing code easier since user doesn't have to
make unnecessary external constants.

Replace one list separator literal with constant
Add lenient mode checks to new function methods
Fix missing space to lenient mode exception texts
Document methods in JavaScriptWriter
Turn off comments in JSON mode
Add lenient mode test for new function call methods