Wrap eunit macros into begin ... end blocks

This makes typos such as missing commas between two assertions
(e.g. ?assert(true) ?assert(true)) syntax errors instead of silently
compiling and failing with a badfun error at runtime.

This won't break any existing code as parenthesed expressions and blocks
have the same precedence and none of these macros can be used as patterns.
Merge branch 'maint'