- Changes to make adding new mapping functions easier

[jnmoyne]

• Adds new subject mapping functions:

{{SplitFromLeft(wildcard index, position)}}
{{SplitFromRight(wildcard index, position)}}
{{SliceFromLeft(wildcard index, slice size)}}
{{SliceFromRight(wildcard index, slice size)}}
{{Split(wildcard index, deliminator)}}

Examples:

	shouldMatch("*", "{{splitfromleft(1,3)}}", "12345", "123.45")
	shouldMatch("*", "{{SplitFromRight(1,3)}}", "12345", "12.345")
	shouldMatch("*", "{{SliceFromLeft(1,3)}}", "1234567890", "123.456.789.0")
	shouldMatch("*", "{{SliceFromRight(1,3)}}", "1234567890", "1.234.567.890")
	shouldMatch("*", "{{split(1,-)}}", "-abc-def--ghi-", "abc.def.ghi")
	shouldMatch("*.*", "{{split(2,-)}}.{{splitfromleft(1,2)}}", "foo.-abc-def--ghij-", "abc.def.ghij.fo.o")

• Subject mapping functions can now be all lower case or Pascal case (or a combination): e.g. splitfromleft, SplitFromLeft, splitFromleft, etc...

• [ ] Documentation added (if applicable)

• [X] Tests added

• [X] Branch rebased on top of current main (git pull --rebase origin main)

• [X] Changes squashed to a single commit (described here)

• [X] Build is green in Travis CI

• [X] You have certified that the contribution is your original work and that you license the work to the project under the Apache 2 license

/cc @nats-io/core

[derekcollison]

Are we going to try to merge this before 2.9 is released?

[ripienaar]

would love to see it merged.