This patch introduces a new export method for sending metrics to
__Riemann__ server using _TCP_ protocol. The module can be enabled like
all the other exports in __Glances__, specifying the `--export-riemann`
option.

Sending metrics to Riemann requires
[bernhard](https://github.com/banjiewen/bernhard) that is
the most popular _Riemann client_ written in python.

In the configuration file you can only specify the `host` and `port`
that riemann is listening for new connections on. Later new options are
planned to be added like __SSL__ support and __UDP__.

Documentation and manpages are refreshed according to the modifications
in the config options and introducing the usage of Riemann export.
Signed-off-by: NGergő Nagy <grigori.grant@gmail.com>

Add missing files to MANIFEST.in
Better package structure
Better path handling

Add missing commands to man page.
Attempt to uniform all the info and use the same conventions all over the
place.