In this PR:
* Temporarily remove all YARD doc config, to be added back
after migrating CI to Github Actions, to simplify config
and dependencies
* Remove all testing and references to < 2.6 Rubies
* Simplify JRuby and TruffleRuby testing to latest stable versions
NOT in this PR:
* Any simplifying code changes that are now possible due to
removing support for EOL Rubies
Closes#58
when the DSL object is the same object as the block context object.
This short-circuits prior to performing setup (like copying ivars
from the block context to the proxy) that is unnecessary when the block
context and DSL object "match".
Add test that runs non-mutative code on frozen DSL object to check that
no FrozenError is raised, as it would have been if a
FallbackContextProxy tried to dynamically add methods to the DSL object.