proposal: more frequent/flexible release dates

[Simon Michael]

I have been doing major releases on the last day of the quarter for two years. Now I'm thinking of relaxing the strict schedule a little, to:

- get useful features and fixes into the hands of users more quickly and more often. I assume a significant number of users will install releases from hackage/stackage but not unreleased code from github.

- keep more in step with the haskell ecosystem. Expanding on https://github.com/simonmichael/hledger/issues/883: GHC is now released every six months; GHC 8.6 arrived just before hledger 1.11. Adding support for that is a big enough change that it should be a major hledger release, but that is not scheduled till 12/31. That would mean three months without a released version of hledger that can support the increasingly popular latest GHC version. That might be ok, but it also means we are excluded from Stackage nightly for a long time, harder to install with stack, and at risk of missing a new stackage LTS release. 

- reduce release work. Counter intuitively I think having a more frequent release window will avoid some work that I might otherwise have to do. 

Proposed new policy: 

- ship major releases when needed/wanted

- but normally at most one major release per month, at least one per quarter

- normal release window is "soon after the start of each month". Eg it could be the 1st, or the 4th, or later (I am usually busy in the first week of october).

[Simon Michael]

PS, and under the new policy I might do a special 1.12 release to support GHC 8.6.1, quite soon.