Use soname libm4ri.so.1

[tornaria]

Resolves #11.

See http://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html for updating the version.

TL;DR where LT_VERSION=c:r:a

• increment "r" each release;
• when interfaces are only added, increment both c and a
• when interfaces are removed or changed, increment c and set a to 0

The soname will be libm4ri.so.$((c-a)), so only the third case will force users to rebuild.

The idea is that libm4ri.so.1.0.* is both backward and forward compatible,
libm4ri.so.1.1.* will be backward compatible but not forward compatible, and
libm4ri.so.2.* will be neither.

[malb]

Ta!