Added --recurse and --trim to cli kv_get

[MWers]

Added --recurse and --trim to cli kv_get as per issue #56.

I had trouble getting argparse to allow 0/1 args for --trim without conflicting with the key. If there's an easy way to do this that I'm overlooking, please let me know.

Here are a few simple examples using --recurse and --trim:

$ consulate kv get --recurse test
test/recursive/KEY_1    one
test/recursive/KEY_2    two
test/recursive/KEY_3    three

$ consulate kv get --recurse --trim 0 test
test/recursive/KEY_1    one
test/recursive/KEY_2    two
test/recursive/KEY_3    three

$ consulate kv get --recurse --trim 1 test
recursive/KEY_1 one
recursive/KEY_2 two
recursive/KEY_3 three

$ consulate kv get --recurse --trim 2 test
KEY_1   one
KEY_2   two
KEY_3   three

$ consulate kv get --recurse --trim 3 test
KEY_1   one
KEY_2   two
KEY_3   three

$ consulate kv get --recurse --trim 99999 test
KEY_1   one
KEY_2   two
KEY_3   three

[gmr]

Looks good, I'll play with argparse and let you know what find.