HTTP/2 streams

Closes #26 and #8

See merge request bortzmeyer/homer!11

Remove short option for debug

See merge request bortzmeyer/homer!15

Short option -d is already in use as the short option
for --delay

Option debug

Closes #25

See merge request bortzmeyer/homer!14

Calculate time for each requests.
Closes #26

See merge request bortzmeyer/homer!13

These tests use curl output to assess if the behavior is
right or not.
However, the curl output can not be reliable in the current
situation where we look for a multiplexed connection, but
curl might have decided to reuse the connection if it is
available.

This allows to establish the connection to the server
and to instantiate the multi interface.
Without this all the handles are created and added to
the multi interface. When we run the multi_perform no
connection is already established putting all the
handles except one in a waiting mode. This seems to
have an impact on the timer of each transfer (they
start too early not reflecting the real elapsed time).

With HTTP/2 streams, multiple transfers occur simultaneously.
The received data is stored in the corresponding handle as it
is received. Then the data is parsed, checked and displayed.
With the --sync option, the data is only parsed after the last
transfer is completed. Therefore all the received data are
parsed, checked and displayed synchronously.
However the data is still received asynchronously.

Catch exceptions

See merge request bortzmeyer/homer!10

Do not use the CurlHandle class to store the curl handle.
Instead, use the `pycurl.Curl` class and add attributes to it.