Try to improve compatibility with system readline libraries

[drroe]

Change the way readline is included so that it is consistent between the internal readline and system readlines. Also add better checks for whether ltermcap or lncurses is needed. Should help the conda package.

[drroe]

python 3.10**  is not installable because it conflicts with any installable versions previously reported.

Have I mentioned before how much I detest python's versioning hell...