Use \b instead of \r for erasing

This allows the spinner to appear at the end of an already printed line
without having to set that as the prefix.
Merge pull request #11 from millere/master

Prevent existence of multiple spinners
add comment for test, remove unneeded output, remove unused import
adjust TestStart to account for the new functionality and raise coverage
small changes
made error var unexported, format change
Merge
Start no longer returns error
Merge
Merge branch 'master' of https://github.com/briandowns/spinner into nocr

Conflicts:
	spinner.go
	spinner_test.go
Switch from carriage return to backspace

Allows for printing arbitrary text through normal means on the same line
as a spinner with expected behavior.
Make more testable

By adding an internal writer field to the spinner, the test can set it
to output to a buffer that can be inspected for expected output,
allowing tests to give better answers. Also could allow for API change
to permit having a spinner on stderr if desired.