loosen unnecessary ABI restriction

[issue reported by Michael Zeilfelder]

-given the low level of development seen on this library, such a
restrictive SOVERSION is unnecessary. changes to ABI would usually
entail a bump at the MAJOR_VERSION level, not the BUILD_VERSION
level
-currently, cmake builds won't be a drop in replacement for consumers
of existing builds, who will be forced to rebuild whole applications
unnecessarily

pre-commit
> readelf -a ./libalut.so.0.1.0 | grep SONAME -
 0x000000000000000e (SONAME)      Library soname: [libalut.so.0.1.0]
post-commit
> readelf -a ./libalut.so.0.1.0 | grep SONAME -
 0x000000000000000e (SONAME)      Library soname: [libalut.so.0]
Merge pull request #4 from elbeardmorez/so.version

loosen unnecessary ABI restriction