Add amount field

[mkalinin]

Adds an amount field by appending it to the end of the calldata, right after the pubkey.

input calldata
+--------+--------+
| pubkey | amount |
+--------+--------+
    48       8

storage
+------+--------------+-------------------------+
| addr | pubkey[0:32] | pubkey[32:48] ++ amount |
+------+--------------+-------------------------+

output memory record
+------+--------+--------+
| addr | pubkey | amount |
+------+--------+--------+
   20      48       8

Depends on #6

[lightclient]

LGTM, I made a few small style tweaks and updated the tests.