Fix / missing free() on some errors


Added doc regarding string encoding for keys


cleaning

gradle 2.14.1 to 4.7
build tools 21.1.2 to 27.0.3
build gradle 2.1.3 to 3.1.3

Patch received in https://github.com/matrix-org/olm/issues/13

Patch has been received by e-mail, Signed-off-by: Arnaud Fontaine <arnaud.fontaine@ssi.gouv.fr>

Signed-off-by: Sophie Taylor <sophie@spacekitteh.moe>

Add functions to make the difference between the native and the java code version.

Factor out the version management in the makefiles.