Unload sounds when destroying MapRenderer

This fixes environment sounds continuing to play after exiting to the
title screen from gameplay.
Remove section "Running flare" from README.engine
Install instructions: add fedora dependencies.
installation instructions: Remove python and standard gcc for openSUSE

There is still gcc-c++ which is enough.
Increase preallocate mixing channels.
Reindent the SoundManager with tabs, add comment to AUDIO variable.
Make use of location based sound for enemy and loot.
Merge pull request #391 from dorkster/bugfixes

Unload sounds when destroying MapRenderer
Merge pull request #393 from stefanbeller/master

cleanup Readme, enhance install instructions.
Merge pull request #394 from hean01/master

Increase of preallocated mixing channels.