Follow project coding style. Issue #2192.
Stop using internal libtorrent API. Closes #2202.
Use parse_magnet_uri() where possible.
Remove useless includes.
Revert "Temporarily disable Travis CI tests against libtorrent 1.0.x until #1878 is resolved."

This reverts commit 7029f4dcd2f123014b93718ee8da68ce8e1558e7.