Merge #73: when base64 is activated enable also elements base64

aaa57fd when base64 is activated enable also elements base64 (Riccardo Casatta)

Pull request description:

  close #71

ACKs for top commit:
  apoelstra:
    ACK aaa57fd

Tree-SHA512: 21b26076c3b4b90d45c72f9341e0c1de14b9e1216017b1b4f7332d5f998dd5b9c74b18696bea524ac62750357d43b522b60a22bfabadbc5e5d738db26ae862f9

Author: apoelstra

Cargo.toml

@@ -16,7 +16,7 @@ trace = []
 
 serde = ["actual-serde", "bitcoin/serde", "elements/serde"]
 rand = ["bitcoin/rand"]
-base64 = ["bitcoin/base64"]
+base64 = ["bitcoin/base64", "elements/base64"]
 
 [dependencies]
 bitcoin = "0.31.0"