Io fixes

[dubek]

Few fixes for the Io implementation (in 4 commits for easier review):

• Fix list and vector equality (this is the issue that broke the self-hosting in Self-host issues related to 'not' or '=' (fantom, haxe, io, nasm, powershell, r, rexx and vala) #418 ); I'll add the new step4 optional tests in a separate PR.
• keyword and symbol accept a keyword/symbol argument (soft fail in step9)
• Don't mutate existing function when defining a macro (soft fail in stepA)
• Atoms can have meta (soft fail in stepA)

[dubek]

I cancelled the full travis build and then restarted the io tests, and they pass: https://travis-ci.org/kanaka/mal/jobs/561626579 .

[kanaka]

Thanks. Merged.