Use a more flexible rubygem requirement syntax (bnc#895069)

https://en.opensuse.org/openSUSE:Packaging_Ruby#Format_of_automatically_generated_Provides:_headers
add tool to easy create maintenance branch in git
release
more secure way to create branch based on latest upstream master
add check to not create such branch on forks
add nice header
Merge pull request #57 from yast/rubygem-requires

Use a more flexible rubygem requirement syntax (bnc#895069)
Merge branch 'master' of github.com:yast/yast-devtools into create_maintenance_branch_script

Conflicts:
	package/yast2-devtools.changes
Merge pull request #58 from yast/create_maintenance_branch_script

Create maintenance branch script
fix build and place correctly script
remove rb suffix
Merge pull request #59 from yast/create_maintenance_branch_script

fix build and place correctly script
use correct build target for SLE 12 maintenance branch
release
Merge pull request #60 from yast/fix_sle_12_bt

Fix sle 12 bt
switch to rubygem() based buildrequires so we can easily switch the ruby version.

( pulled from https://build.suse.de/request/show/41434 )
fixed up an old changelog entry, added author
Merge branch 'darix'

Conflicts:
	package/yast2-devtools.changes
	package/yast2-devtools.spec

Resolved in favor of using
   rubygem(foo)
instead of
   rubygem(%{rb_default_ruby_abi}:foo)
version + changelog
Merge pull request #61 from yast/merge-ibs

Resolve IBS conflict.