readme updates
short error message for unknown command

The full help text is long enough to be really annoying
now, especially if you're in the middle of something and
merely made a typo.
suggest spelling corrections for mistyped commands
Fix for shorthand db name args (i.e. "rose")

Thanks @dpiddy!
grab full bins for diff in parallel
fix for parallel diff generation
tests to ensure PX dyno scale works
show dyno size in hk dynos

Fixes #72.
fix ensureSuffix
fix arch detection for linux users

Fixes #74.
Revert user.Current().HomeDir to os.Getenv("HOME")

user.Current() requires cgo and thus doesn't work with cross-compiling.
This appears to be how the Heroku Toolbelt works, though per @fdr it may
not be correct for all cases (when users have modified their home dir).

We will address those issues if/when they come up.

Also moved these functions to util.go
Move homePath() and netrcFilename to platform files.

Gets them properly defined at build time instead of switching on
runtime.GOOS at runtime.
Easier to change install location.
s/iif/if/
don't need to append 'X' suffix to dyno sizes anymore
styleguide update
suggest help topics as help commands

fixes #78