Made the util::Dir append function const safe
Added const specifier to asset_dir argument of audio_manager's
load_resources method
Implemented JobManager to load gamedata resources

The game loads straight away without waiting to load the gamedata and
once the data is loaded continues to behave as it has been doing before
this commit.
Fixed the intialization reorder compiler warning
Merge branch 'master' into gamedata-job

Conflicts:
	copying.md
	cpp/game_main.h
Made the on_gamedata_loaded function accept reference to gamedata
Made GameMain a friend of Engine

This can be removed once all the components have been properly moved
from GameMain.
Showing a text saying that the gamedata is loading
Merge pull request #137 from jprashanth/gamedata-job

Fixes #70
 Units created as a general game object class
-- Units have a stack of actions
-- the top action decides the graphic and change of state
-- Units have abilities (abilities create actions)

The unit movement uses path finding
-- pathfinding initiated with start and end tiles
-- a star takes a lambda function to decide what is passable
-- if blocked a unit finds a new path
-- intersection tests for many units on a single tile
-- ending at the nearest reachable point when cannot reach target

Terrain object split over several classes
-- terrain object will represent a space on the terrain
-- there are square spaces and radial spaces
-- the building specific items are moved to the BuildingProducer class

Units have outlines on terrain
-- generated on startup
-- squares made using foundation size of building
-- circles made using radius of units
path smoothing
Merge pull request #69 from Jon0/master

epic: basic action stack, and a unit moving around.
convert: split up game specification code generation
Merge pull request #155 from TheJJ/convert-splitup

convert: split up game specification code generation
release: new minor release achieved

now supports walking units!
convert: fixed function imports from util module

sound conversion was broken because of that.
Fix path.cpp compilation error in mac clang
Merge pull request #162 from jprashanth/mac-clang-issue

Fix path.cpp compilation error in mac clang
readme: fixed opusfile build dependency for fedora

this fixes #164
readme: beautified the build instructions