support for getting scriptPubKey

[soy-sauce-rice]

Hello, I think this is a good library, I can use this library to generate address and signature transactions.
But I don't know if you have the function of get scriptPubKey.
Privkey and scriptPubkey are required for signing transactions.
I can get privkey from your program, but scriptPubkey needs to be obtained from the bitcoind program.
My approach is this:
1 Get pubkey and privkey with bitcointool
2 bitcoin-cli importprivkey <privkey>
3 bitcoin-cli validateaddress <pubkey>
So that I can get scriptPubkey.
Do you have an easy way to get scriptPubkey?

[xloem]

script.h provides for building signatures (scriptpubkeys).

• btc_script_build_p2pkh, btc_script_build_p2sh.
• a btc_script_get_script_from_address func on the wallet_new branch looks like it is pending porting from c++ which i might be able to finish. it might be there to aid in debugging an error. it appears to be a slightly old version of code from bitcoin core's key_io.cpp

ecc_key.h appears to generate hashes for these sigs, from pubkeys. bitcointool outputs these hashes when asked for addresses.

• btc_pubkey_get_hash160
• btc_pubkey_getaddr_*

#100