make nmea-parse more embedded feasible

[xMAC94x]

Hi @zaari, I am looking for a nmea parser for a GPS project. Concrete its about an ESP32-S3 interpreting GPS. From docs your crate looks quite promising, but currently I cannot compile it as it builds on bitvec which itself builds on radium 0.7´, which requires AtomicU64` which my platform doesn't have :/

Additionally I was wondering if it would be possible to get rid of the HashMaps - this however is not a requirement, just a though to reduce memory footprint and dependencies.

Just want to start a discussion if this project is still active and such PR are welcome or not, before i start coding on it ;)