Rearrange includes
Fix english and indentation
Force to 80 columns
Add 1-way delay measurement
Move forward declaration in front of the file
Update Doxyfile
Coding style
Move doxygen comments inside of #ifdef
Update comments
Variables are only used in one file. Make them static
Force to 80 columns
Unique identifier for intermediated interval report columns

In the current implementation it was very error-prone to add a new column to
the intermediated interval report, because of the state of intermediated
interval report was widely spread around different arrays with different sizes.

Now we have 'one' array that tracks everything: the name and unit of the column
as well as the status (visibility, column width). Moreover, each column has now
a unique identifier. We can now easily address ever column directly instead of
an error-prone looping.
Update todo
Rearrange enum location
Move usage*() and init*() in front of the file
Move parse*() in front of main()
Move guess_topology() near to report_final() (where it is used)
Move sigint_handler() near usage() (like flowgrindd)
Move log_output() to the beginning of the file
Move shutdown_logfile() near to init_logfile()