Add test/parser.block-expressions.
Refactor: Load grammar, generate parser, and parse stuff inside it() clauses in test/parser.block-expressions.

Mocha blows the whole test execution if something is thrown in describe() clauses or in global test scopes :(

Doing everything that can fail inside it() clauses at least helps pinpoint which test file is throwing.
Refactor: Do the same in test/parser.empty-program.
Refactor: Prefix tests with numbers so that they run in order.
Refactor: Rename 'start' grammar rule to 'Program.'
Make test/001.parser.block-expressions pass.
Add test/001.parser.block-expressions 0 child expressions test.
Make test/001.parser.block-expressions 0 child expressions test pass.