865ba3fc39 Move serde string macros to internals (Tobin C. Harding)
4a2b13fcde internals: Feature gate whole serde module (Tobin C. Harding)
Pull request description:
The macros are internal things and can live in `internals`. This will help with future crate smashing.
ACKs for top commit:
apoelstra:
ACK 865ba3fc39
Kixunil:
ACK 865ba3fc39
Tree-SHA512: 7b3f029206c690ecf2894e0ad099d391312f7f8ec65ac9b5d4d9f25e6827f92075dcc851d0940a0faf1e27e7d0a305b575c8cc790939b3f222d7a2920d4d24fe