UBUNTU: Make printchanges/insertchanges work with Endless release commits

For endless, the commit subject will be 'UBUNTU: release x.y.z' instead
of 'UBUNTU: Ubuntu-x.y.z'. Detect that option to get the changelog
handling to work again.

[endlessm/eos-shell#2840]
UBUNTU: release 3.13.0-27.50endless2

[endlessm/eos-shell#2840]
UBUNTU: Start new release

Ignore: yes

[endlessm/eos-shell#2840]
UBUNTU: Add new rules target for generating endless release

startnewrelease doesn't work with our local endless package revision
suffix, so add a separate rule "startnewendless" that just bumps the
local revision up.

[endlessm/eos-shell#2840]
UBUNTU: Add README.endless doc describing packaging process

We handle linux a little differently than our other packages, so add a
little documentation describing the packaging flow.

[endlessm/eos-shell#2840]
UBUNTU: release 3.13.0-27.50endless3

[endlessm/eos-shell#2840]
Merge pull request #2 from endlessm/shell/2840

Fixup handling of git repo and document process