Fix use of errors in various commands

Some used errors but didn’t import the error module; others _vice
versa_.

One was throwing a generic error instead of a CommandLineError.
Fix some comment and message typos
Merge pull request #198 from rrthomas/interpolate

Fix use of errors in various commands
Merge pull request #199 from rrthomas/interpolate

Fix some comment and message typos
Add bash-completion code for metapolator
Merge pull request #200 from rrthomas/interpolate

Add bash-completion code for metapolator
Add bash-completion to Vagrantfile
Merge pull request #202 from rrthomas/master

Tweak link to make it clickable in text editors that append the close paren
Merge pull request #204 from rrthomas/interpolate

Add bash-completion to Vagrantfile
Use console.warn for warnings/diagnostics

So as not to interfere with output (console.log) when using the command
line.

Closes #203.
Merge pull request #205 from rrthomas/interpolate

Use console.warn for warnings/diagnostics
Interpolation command

Takes a list of masters and a list of proportions, and spits out
CPS (based on that written by Lasse for his initial demo) that
interpolates the given fonts with the given proportions.

To use the output, redirect it to a new .cps file under
data/com.metapolator/cps, and add a new master entry to project.yaml.

Or wait until I add this functionality myself.
Merge pull request #206 from rrthomas/interpolate

Interpolation command
Add --port argument to red-pill; default is random

Depending on your OS, the default port may be guaranteed not to clash
with an existing server (if one is available), or may simply have a good
chance.