Update licence header
Create an auxiliary directory for autoconf tools
Improve the detection of a compatible BSD Make program
Factorise program detection
Hardcode the name of the GPG program used
Soften the dependance on GPG and GraphicsMagick
Enhance feature control
Modernise the use of AC_OUTPUT
Improve detection of the system user identity
Rework detection of compression tools
Reorganise file
Merge branch 'topic/rework-configuration'