This makes the Element ID a fixed part of the Error.
The ID can probably be turned into an `Option<NonZeroU32>`
at some point, but that feels like a low priority.

- Refactor ebml_generic for better readability
- Add lifetime parameter to EbmlParsable
  This allows implementing the trait for borrowed types
  like &[u8] (binary_ref).
- Add `fn has_crc() -> bool` to trait EbmlParsable
  Also adds CRC-32 capabilities to ebml_generic, making it
  functionally equivalent to the master helper function when
  has_crc returns true.
- Rename ebml_generic to ebml_element
  It can now handle most EBML Elements without issue, so
  the new name is more descriptive.

**This breaks compilation for elements.rs**, because
matroska_permutation was changed (again) and it's not
worth fixing this when the macros can soon be used instead.

The macro `impl_ebml_master` will
1. create a pub struct definition with the given field names/types
   and any meta (like #[derive] blocks) and
2. implement EbmlParsable for the aforementioned struct. This
   implementation will set the has_crc() to true (to use the new
   ebml_element feature) and create a try_parse definition based
   on matroska_permutation. It will auto-"unwrap" the parser results
   and handle any parsing errors. It also handles Option<T> and Vec<T>.

There's no such thing as "single-element tuples", so the
macro-implemented `impl Permutation` blocks don't work for
singular Parser functions. So, here's a manual implementation.

- Use impl_ebml_master to define all Matroska Master Elements
- Change sub_element helper to make it similar to ebml_element,
  but still work in the SegmentElement context.
- Adapt segment_element fn to the sub_element changes.
- Add note to fix what used to be correct Float Element handling
  (used to be float_or)
- Small fix in the macro (lifetime-related)
- Comment out/remove the unimplemented Elements Chapters, Tags,
  Attachments and Cues (should be added back later)
- Edit serializer/muxer/demuxer stuff so it works again after the changes

They were pub before (and in the crate root).