js: Add callingConvention setting

For now it defaults to the existing behavior "by-position-only" and changing it
has no effect.
js: Don't include params if method is called without arguments
js: Add by-position-or-by-name calling convention

Fixes #699
docs: Add ncmpcpp library view slowness workaround

Based on comments in #727.
Merge pull request #746 from jodal/feature/js-calling-convention

Add by-name calling convention to Mopidy.js
docs: Fix broken reference
docs: Fix duplicate cmdoption usage
docs: Add more details on Mopidy.js calling convention
docs: Changelog tweaks
docs: Lift manpage a level up since we only have one command now