Replace Release Managers Guide (RMG) with new version:

Replace Release Managers Guide (RMG) with new version:

Many of the mistakes made by me during a release has to do with the
confusing instructions in the guide.

* Some steps are mentioned in different order
* Some steps are mentioned (and noted to *NOT* do)
* The confusion between "MAINT" and "BLEAD-FINAL", and "BLEAD-FINAL"
  and "BLEAD-POINT".

This generator generates a checklist with only the instruction you
*will* have to perform. Any steps that mentions they must be skipped
for the release will not be included in the end-result.

Unlike the previous guide, you need not know the type of the release
you do. Instead, you give the version you want to release and it
generates the appropriate one for you.

All the following incantations work:

    perl Porting/make-rmg-checklist --version 5.26.0-RC2 # RC
    perl Porting/make-rmg-checklist --version 5.26.0     # BLEAD-FINAL
    perl Porting/make-rmg-checklist --version 5.27.0     # BLEAD-POINT
    perl Porting/make-rmg-checklist --version 5.27.1     # BLEAD-POINT
    perl Porting/make-rmg-checklist --version 5.26.1     # MAINT

Extra benefit: Apparently it includes additional checklist steps
at the top that somehow are not included when you currently generate.

Downside: HTML is not yet supported.