History of Coding style

Fix logic typo ("somethingthatshouldbetrue" meant to say "somethingthatshouldbefalse") in NS_WARN_IF documentation. The point is that we warn [and return an error code] if the thing is unexpectedly true.

Fixed missing code highlight

Add comment about constructor member init

Add "e" prefix for enum values in c++ code

Add SVG guidelines

clarified: 'forward declare' --> 'forward-declare'

Revert r802167 since there wasn't agreement and it goes against the common style of browser/ and toolkit/

Added caveat that you should still use "NS_" prefix on macros if your new macro is part of a set still using that prefix