Update notification for release 0.43

Based on @pthiess's original draft plus the [release notes](https://github.com/adobe/brackets/wiki/Release-Notes:-0.43) draft.

CC @ryanstewart @dangoor @njx in case you have feedback.

Also -- added README instructions for testing JSON changes like these in-situ in Brackets.
@JeffryBooher That reference is talking about cases where the quotation mark is part of the string being quoted, which isn't the case here.  Afaik putting punctuation outside a regular quote is generally considered incorrect by most style guides like AP, MLA, NYT, etc.  But it's a popular 'mistake' and I see we've already done so once before in an earlier notification, so I'll switch it if that's what everyone wants...