initial macrodef documentation
Make `with` return the last expression from its branch

Thanks @rwtolbert for the bug report
better macro example
documentation for global
fix to assoc docs + new multiassoc definition
documentation for require
working on documenting macros
cond documentation
working on documenting builtins
clarified rest / cdr, cleaned up require
Merge branch 'master' into pr/258
Merge branch 'master' into pr/263
Merge branch 'master' into pr/262