Add ccache support

[davetcoleman]

Closes #87

@ahoarau seems we need to do other things to enable ccache, like tweak the catkin command or... ?

[ahoarau]

Yup, this happens when ccache is configure as :
export CXX="ccache g++-5" CC="ccache gcc-5"
Which is how most people configure it afaik

[davetcoleman]

I'll assume you approve this, merging

[VictorLamoine]

For your information this is how ccache is supposed to be configured: https://askubuntu.com/questions/470545/how-do-i-set-up-ccache?answertab=active#tab-top

[ahoarau]

Thanks ! I remember reading somewhere than " masquerading " (symlinks) were not recommended. I'll try this though. I have the feeling that it will be seen by cmake as g++, which is much better than /usr/bin/ccache g++