[QGIS-Developer] Changelog for 3.10

[Nyall Dawson]

Hi list,

Once again a release has rolled around with our changelog in complete
disarray. :(

I w̶a̶s̶t̶e̶d̶ invested some time today copying entries from the git
log across to the changelog, but honestly, we were all TERRIBLE this
cycle and the git commits for features consistently had next to no
documentation. Everyone was at fault here*.

As a result, the changelog still looks... rather... crap. So devs--
please fix and expand on your entries!*

As a reminder from last cycle, we've adapted certain language
guidelines to make the changelog consistent and easier to read:

- Don't use passive tense "A feature was added which allows use
of...", instead replace it with the more personal "WE added a
feature... this allows YOU to...".

- Talk up features! Make them sound innovative, exciting and "fun",
instead of dry and technical.

- Give lots of credit to sponsors, e.g.  "In previous QGIS versions
you had to ... . Now, thanks to sponsorship from ###, you can now
directly import..."

Nyall


* myself included