Add STL32L496xG support

[hs-olp]

Just as #142, We've been using this library (and your bootloader) for our boards for quite a while and Management approved a move to upstream our additions. The commit was rebased to both reflect who did the actual work at our place and to obviously be on top of your master. Should you prefer me doing something else, I'm of course willing to do so.

Tested on a number of in-house boards using this uC for years for use with your bootloader without a problem.