Make executor emulate putchar

Fixes #1056.
javascript: inline conditions
Merge pull request #1177 from david-christiansen/issue/1056

Make executor emulate putchar
javascript: remove some more constructors
Merge pull request #1178 from raichoo/javascript

Javascript
Bring module loading into Idris monad

This allows proper error signaling, compared to IO, which is important
for IDESlave
Follow IDESlave protocol when import not found
Make ihWarn work properly with emptyFC on command line
Prevent double-printing some FCs
Merge pull request #1180 from david-christiansen/ideslave-message-fix

Make missing imports errors follow the IDESlave protocol