Add descriptions to instruction set.

I used src/carp_instructions.c to fill in the remainder of the
documented instruction set.
Add another Carp example.

This example prints out a countdown from 10 using a jump instruction.
Merge branch 'add-readme-doc' of https://github.com/jbcrail/carp
Merge branch 'add-carp-example' of https://github.com/jbcrail/carp
no int! carp_value!
add CDEBUG option for printing state, fix jump related issues