[SFrame-V3] libsframe: bump so version to libsframe.so.3.0.0

Consolidate the 2.0 and 2.1 nodes into a new 3.0 node.

In subsequent patches for releasing SFrame V3, libsframe APIs will be
affected.  A non-exhaustive list of noteworthy changes are mentioned
next.

Some existing APIs (breaking binary compatibility) by adding an
additional arg to these:
  - sframe_fre_get_ra_offset
  - sframe_fre_get_fp_offset
  - sframe_fre_get_cfa_offset

Change of argument type:
  - sframe_find_fre

The behaviour of some APIs will change:
 - sframe_encoder_write now writes out V3.

And lastly removal of two APIs:
  - sframe_decoder_get_funcdesc
  - sframe_encoder_add_funcdesc

Above make this release of the library binary incompatible with previous
release, hence a version bump and new version node 3.0.

Reviewed-by: Jens Remus <jremus@linux.ibm.com>

libsframe/
	* libsframe.ver: Create a new 3.0 node.  Remove the 2.0 node.
	* libtool-version: Bump the so version.