neubot.1.rst: bump copyright
neubot.1.rst: bump date of last update
neubot.1.rst: add forward reference to SUBCOMMANDS section
neubot.1.rst: document more precisely the test selection process
neubot.1.rst: clarify that speed depends on the latency
neubot.1.rst: document how to invoke the dashtest

More options are available than the ones I documented, I'm just
documenting the ones shared with other tests so that all tests have
exactly the same command line interface (which is nice and good).
neubot.1.rst: better -6 and /var/{,lib}/neubot documentation
neubot.1.rst: better documentation of usage examples
neubot.1.rst: do not vaguely list bugs in the manpage
doc/neubot.1.txt: clarify raw test data format
neubot.1.rst: document the dashtest data format

While there, also globally get rid of spaces at end of line.
neubot.1.rst: improve my rst
neubot.1.rst: improve dashtest description
Merge pull request #21 from bassosimone/feature/improve_manpage

Improve Neubot's manpage