Re-work temp file handling

Remove the additional layer of indirection, and track temporary files
and directories right after they are created.
[Fix #99] Make `source` preserve the buffer file name

Resolves a blocker for #122.
Fix creation of temporary directories

`make-temp-file` can create directories, too, so let's make use of this
feature.
Install `install-info` in testing VMs

Required to run `make doc` successfully on Travis.
[Fix #122] Add Erlang syntax checker
Add command to google messages at point.

Requires the Google This library by @Bruce-Connor at
Bruce-Connor/emacs-google-this.
Document package repo for Google This
Release 0.10
[Fix #123] Teach the ruby checker about warnings

The warnings generated by the interpreter always start with `warning: `,
unlike errors that have no prefix.
Colorize mode-line depending on Flycheck status.