add t/README.md as a guide to testing
Rename TestMLBridge to TestBridge

Eventually, this will contain all testing functions, not just
TestML ones.
Move yaml_ok() into test_yaml_perl()

This function was only used once, so this commit inlines it into
the TestBridge
Converted 03_regression into tml-local tests
have TestMLTiny skip junk lines after single-line points
migrate yaml_error() tests to .tml
this didn't get changed when bridge class was renamed
fix testml for new bridge
Consolidate and reorganize read() tests

Read tests were scattered and are now in a single .t file.

Moves t/data/51491... to t/tml-local/nesting.tml as it is a parse test,
not an encoding test, so can be a .tml file

Removes t/data files now tested in t/tml-world.  Renamed t/data/one.yaml
to ascii.yaml for clarity of purpose Converts one remaining untested
file into t/tml-local/documents.tml

Also simplifies some of the multibyte/BOM data files to just
the relevant data that might cause problems.
remove unused load_ok test function
moved remaining test functions to TestBridge
consolidate write() tests
Consolidate read_string tests.

Created a file for read_string tests that can't be done via .tml and
moved relevent tests there.

Deleted duplicate tests.

Moved one syntax error test to load-errors.tml.
YAML.pm compatibility testing

Renamed file with compatibility tests for clarity.

Fixed up error test to use error_like().
fix error_like function to respect test label argument
Allow YAML without trailing newline
cover read/read_string as object methods
put 11_read_string.t tests into subtests
covered and fixed error message for invalid UTF-8 strings
note a parsing clause as unreachable and uncoverable