Build by default with optimization level -O2 for GCC

before -O0 was used by default, that caused pretty bad performance.

Amd64, i6700k, 4200MHz, GNU/Linux (non-RT kernel), gcc 7.2.0

-------------------------------------
Optimization | EN/ENO |no EN/ENO |
-------------------------------------
default | 11 | 9.5 |
-O3 | 3.9 | 5.2 |
-O2 | 4 | 4.8 |
-Os | 4.1 | 3.5 |
-Ofast | 3.9 | 5.2 |
-------------------------------------

ARM, BBB Cortex-A8, 600Mhz, GNU/Linux, gcc 4.6.3

-------------------------------------
Optimization | EN/ENO |no EN/ENO |
-------------------------------------
default | 273 | 226 |
-O3 | 141.8 | 106.2 |
-O2 | 142 | 107 |
-Os | 152.5 | 112.2 |
-Ofast | 141.7 | 106.2 |
-------------------------------------

For embedded systems with size constaints (like Cortex-Mx, AVR and so
on) I usually use -Os. It gets pretty good results. For
GNU/Linux-based systems -O2 is usually a good choice, as you see the
test results.

Beremiz installation 
====================

Windows
-------
Download installer, install. 

Linux
-----
Pre-requisites::

    # Ubuntu/Debian :
    sudo apt-get install python-wxgtk2.8 pyro mercurial
    sudo apt-get install build-essential bison flex python-numpy python-nevow

Prepare::

    mkdir ~/Beremiz
    cd ~/Beremiz

Get Source Code::

    cd ~/Beremiz
    
    hg clone http://dev.automforge.net/beremiz
    hg clone http://dev.automforge.net/plcopeneditor
    hg clone http://dev.automforge.net/matiec

Build MatIEC compiler::

    cd ~/Beremiz/matiec
    ./configure
    make

Build CanFestival (optional):: 

    # Only needed for CANopen support. Please read CanFestival 
    # manual to choose CAN interface other than 'virtual'::

    cd ~/Beremiz
    hg clone http://dev.automforge.net/CanFestival-3
    
    cd ~/Beremiz/CanFestival-3
    ./configure --can=virtual
    make

Launch Beremiz::

    cd ~/Beremiz/beremiz
    python Beremiz.py