Add optional keyword arguments to deref

The keyword arguments allow support of bashes parameter substitution modifiers,
-, :-, =, :=, +, :+, ?, :?.
Simplify src line comment handling
Allow for unnamed functions in exception message
Updated project.clj, release notes and readme for 0.8.0-beta.3
Merge branch 'release/0.8.0-beta.3'
Merge tag 'stevedore-0.8.0-beta.3' into develop

stevedore-0.8.0-beta.3
Updated version for next release cycle