Issue 10/correcting compilation warnings

[diseraluca]

Resolves #10.

• The modular bitfield crate produces an unneccesary braces warning when From
  implementations are generated.

  See: Remove the unnecessary braces around From implementations. Robbepop/modular-bitfield#66

  A pull request ( Removes the unused braces warning in the autogenerated From implementations. Robbepop/modular-bitfield#68 ) to
  resolve this was provided.

  Since it is not yet accepted mainstream, the modular-bitfield dependency was
  temporarily moved to a custom fork to move forward with the removal of
  compilation warnings.

• Previously, Buildup calculated the crc by digesting data as it was used.
  For this reason, it contained a crc field to keep track of it.

  This was later changed to reduce the state that was kept during a Buildup,
  calculating it in place when the last frame of a transfer and its crc are met.

  The previous code was only commented out and the field containing the crc was
  kept, producing a dead code warning.

  The crc field is now removed from Buildup, and the commented code that
  referred to it was removed.

• The modular-bitfield crate, by default, generates a series of getters and
  setters method for each field.

  When those are unused, a dead code warning is produced.

  To avoid the warnings, appropriate #[skip] attributes for the field of
  various structures were added.