Update the ELF soname not to say "libtinycbor.so.0"

Since we're not (yet) guaranteeing binary compatibility, let's use 0.5
as the "soversion".

This changes the version number stored in the VERSION file so that the
actual library file is "libtinycbor.so.0.5.0". As an indirect
consequence, the release will be tagged "v0.5.0", which sorts after
"v0.5-beta1".

Signed-off-by: Thiago Macieira <thiago.macieira@intel.com>