Fix references to NETCAPTURE_HOST

Initially the program was called `netcapture`. However I changed the
name but forgot to change all its occurences. The environment variable
`NETCAPTURE_HOST` is now named `NETREDIRECT_HOST`.
Add a simple acceptance test + Travis

The test listens on the port 8888 and sends some data to it using
`netredirect`. If the transmission is correct then the test passes.
Otherwise it results in a failure.

The repository is integrated with Travis CI. The build status is
reported in README.md.
Add installation and improve test

By running `make install` the program can be installed in the system.
The procedure is described in `README.md`. Additionally the `test`
script was adjusted to work without installing the software. The
`LD_LIBRARY_PATH` environment variable tells it to look in the current
directory for libraries to preload.