import rlp from package
Merge pull request #30 from brainbot-com/fix_import_rlp_test_error

import rlp from package
add travis-ci
fix: travis-ci image in readme
copy & paste the exact text from travis
travis status image still not ok, while the status in the travis site is OK
fix: the travis image is linked to pyethereum from brainbot-com
use nibble instead of hex for half byte