Make filename positional argument not mandatory

This is ongoing work so that a -l/--list-commands argument can be
used without the need to specify a file.
Rework help and error message from -c argument

This is ongoing work to allow a -l/--list-commands argument.
Add -l command line argument

This argument lists all possible commands with their description
to ease the usage of it.
Merge branch 'list-argument'
Fix Python 3 compatibility

Use only write mode instead of write and binary (the default for
NamedTemporaryFile)
Use a context manager to auto-close the test file
Improve commands docstrings
Docstrings must end with a period
Show help when no command line arguments are given
Update README
First version without tests
Adapt tests to newer queue peaks output
Merge branch 'improved-cmd-queue-peaks'
Add a get_ip method to HaproxyLogLine

This helps standarize how to get the IP on HaproxyLogLine.
strip() returns a new string

It must be assigned to a variable.
Show also the private methods on HaproxyLogFile
Fix docstring
Add references to methods
Minor nitpicks
Rename argparse arguments switchs

Rename -f (--filename) to -l (--log): this way -f is free and can
be reused for --filter.

Remove the -l (but keep the --list-commands) to keep consistency
with future --list-filters which will not have a single character
switch.

Adapt tests, methods and such to it.