…ammar.md document it more fully.

…rk_lark.py (trailing whitespace in test_06_*())

2. Remove what was left of "Literals can be one of: ..." under "Terminals" in grammar.md.

3. Address @erezsh's point about inlined terminals under "Terminals" in grammar.md.

4. Remove "lark.lark-ORIG" references in test_lark_lark.py and test_grammar_formal.py that shouldn't have been pushed.

5. Address @erezsh's point about f.readlines() in test_grammar_formal.py.

6. Address @erezsh's point commented-out tests in test_grammar_formal.py.

…a visitor that enforces some of its restrictions.

…alue in lark.lark'

… they can be inlined.

…with a nice message.

…_grammar does.

…ers and priority, like load_grammar does