python-eventlet & python-greenlet: add new packages

[ja-pa]

Maintainer: me
Compile tested: Turris Omnia (TOS6), OpenWrt master
Run tested: Turris Omnia (TOS6), OpenWrt master

Description:
This PR adds new package python-eventlet and its dependecy python-greenlet.

Eventlet is a concurrent networking library . more info

Greenlets are lightweight coroutines for in-process concurrent programming. more info

[ja-pa]

Rebased
python-eventlet updated to 0.30.2

[BKPepe]

@jefferyto and @commodo can you I ask to review this, please?

[commodo]

i remember the greenlet package;
it was out-of-tree for a while, but required some tuning for the Python package to build it;

i think i broke it a while :p
#518

just as a note; it seems to compile on MIPS from what i can tell;
@kostko is this interesting for you these days?

[commodo]

from my side this looks good;
we can probably wait a while to see if we get any replies on the MIPS side;
but if there is some hurry to have this available sooner for testing, i don't mind to merge and bump the PKG_RELEASE for MIPS;