Simple http server for JSROOT

Can be used to serve JSROOT and ROOT files on localhost httpserver.

1. Checkout jsroot in working directory like ~/work:

    [shell] mkdir ~/work
    [shell] cd ~/work
    [shell] git clone https://github.com/root-project/jsroot.git

2. Copy some ROOT files to files sub-directory:

    [shell] mkdir ~/work/files
    [shell] cp $ROOTSYS/tutorials/hsimple.root ~/work/files/

3. Start server from working directory:

    [shell] cd ~/work
    [shell] python3 jsroot/server/server.py

4. Open ROOT file in JSROOT with the link:

     http://localhost:8000/jsroot/?file=../files/hsimple.root&item=hpxpy&opt=colz

5. Also test examples.htm and api.htm:

     http://localhost:8000/jsroot/examples.htm
     http://localhost:8000/jsroot/api.htm