UltiSnips: add an option to comment non-required options.

[gjherbiet]

This adds the --comment-non-required option to UltiSnips/generate.py with effect to:

1. suppress the blank line between required and non-required options
2. prefix a comment ('#') symbol before non-required options.

Before:

snippet add_host "Add a host (and alternatively a group) to the ansible-playbook in-memory inventory" b
ansible.builtin.add_host:
	name: ${1:# The hostname/ip of the host to add to the inventory, can include a colon and a port number.}

	groups: ${3:# The groups to add the hostname to.}
endsnippet

After:

snippet add_host "Add a host (and alternatively a group) to the ansible-playbook in-memory inventory" b
ansible.builtin.add_host:
	name: ${1:# The hostname/ip of the host to add to the inventory, can include a colon and a port number.}
	#groups: ${2:# The groups to add the hostname to.}
endsnippet

This is useful as all unused (left commented-out) non-required options can then be quickly removed in Vim with the following sequence:

{ V } " visually select the current pagraph = inserted module snippet
:'<,'>g/^\s\+#/d " command to delete all lines beginning with spaces/tabs and the comment symbol in current visual selection

[pearofducks]

Can you resolve the conflict here from #128 and then I'll bring this in too?

[gjherbiet]

Conflict resolved. You can proceed with the merge. Thanks.