Allow cct to instantiate operations via object codes or names

[kbevers]

Possible fix for #2418

• Closes cct can't instantiate operation given as urn:ogc:def:coordinateOperation:auth::code #2418
• Tests added
• Added clear title that can be used to generate release notes
• Fully documented, including updating docs/source/*.rst for new API

[kbevers]

With d266b21 it is possible to do

$ echo 3541657.3778 948984.2343 5201383.5231 2020.5 | PROJ_LIB=./data/ ./src/cct EPSG:8366
 3541657.9112    948983.7503  5201383.2482     2020.5000

$ echo 3541657.3778 948984.2343 5201383.5231 2020.5 | PROJ_LIB=./data/ ./src/cct "ITRF2014 to ETRF2014 (1)"
 3541657.9112    948983.7503  5201383.2482     2020.5000

$ echo 3541657.3778 948984.2343 5201383.5231 2020.5 | PROJ_LIB=./data/ ./src/cct +proj=noop
 3541657.3778    948984.2343  5201383.5231     2020.5000

$ echo 3541657.3778 948984.2343 5201383.5231 2020.5 > a
$ echo 3541657.3778 948984.2343 5201383.5231 2020.5 > b
$ PROJ_LIB=./data/ ./src/cct +proj=noop a b
 3541657.3778    948984.2343  5201383.5231     2020.5000
 3541657.3778    948984.2343  5201383.5231     2020.5000

$ PROJ_LIB=./data/ ./src/cct "ITRF2014 to ETRF2014 (1)" a b
 3541657.9112    948983.7503  5201383.2482     2020.5000
 3541657.9112    948983.7503  5201383.2482     2020.5000

$ PROJ_LIB=./data/ ./src/cct EPSG:8366  a b
 3541657.9112    948983.7503  5201383.2482     2020.5000
 3541657.9112    948983.7503  5201383.2482     2020.5000

I haven't been able to break existing functionality yet, so I think this could be the way to do it.