Added flag descriptions with the help of soroushjp in #2.
Added optional flag to specify output index in unspent input transaction. Defaults to 0 (first index)
Merge pull request #3 from soroushjp/input_index_flag

Added optional flag to specify output index in unspent input transaction.
Add testnet support with --testnet flag. Resolve #5
Moved base58check to its own package to avoid adding base58check.go to go run commands and separate out helper package base58check