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
Merge branch 'master' into default_hkpath

Conflicts:
	unix.go
	windows.go
Remove dependencies of os/user