autotool 1.12 bugfix

'configure.ac' needs to be updated in order to compile on OSX.
autotool update
column insert with ttl implementation

The function `cassie_insert_column_ttl' was added to support columns insert
with expiracy. The previous `cassie_insert_column' now calls this new function.

`example/cassie_simple.c' was updated to use ttl.