Add HighLine for platform independant shell width

The HighLine gem provides a platform independant way of obtaining
the number of columsn in the terminal. This commit also changes
the way the 'CLR' constant is initialised in Windows to account
for the size of the terminal.
Woops, remove "require 'curses'" in test
Remove JRuby from Travis CI tests

Upstream issues[1] with getting terminal size are causing tests to
fail. Until this is fixed upstream, spinning_cursor will not work
in JRuby.

[1] https://jira.codehaus.org/browse/JRUBY-6693