Correct getrawmempool verbose fee field.

The fee field of the getrawmempool RPC JSON response should be in Bitcoins
instead of Satoshi.  This commit corrects that issue.

Also, add a couple of comments and fix a comment typo while here.
Display float values with btcctl with %f.

This commit modifies btcctl to show float values with %f instead of the
default %v.  This means the values will show similar to 1180923195.260000
instead of 1.18092319526e+09 (scientific notation).