#16 Missing libtool libversion flag bump for new APIs

[Daniel Macks]

Going from libmms 0.5 to 0.6.2, I see several new functions added to the public .h (and nothing removed or altered...thanks for retaining backward-compatibility!). Libtool's -version-info flag is intended to signal what (if any) types of interface changes are made (it's a library/interface versioning value, independent of the source version/release), but 0.6.2 has the same -version-info 0:2:0 (in src/Makefile.am libmms_LA_LDFLAGS) as 0.5 (signifying no change to the interface). This versioning is important for downstream packagers and end-users so that they don't as easily downgrade their library and break things built against the newer version.