chore: add `LICENSE`

Despite referring to a "LICENSE" file in the README, I never made such a
file. Oops.

refactor: `main.zig` require `huffman.zig` only

chore: fix resource link to Wikipedia

refactor: `xcoding.zig` imports `huffman.zig` only

chore: remove depth tracking in tree creation

(1) Did not track depth as one would expect; tracked depth from leaf
instead of root. (2) Information was no longer in use by any code.

refactor: modularize tree logic

refactor: modularize frequency logic

chore: update README and bump version

fix: incomplete decoding

File decoded stopped prior to encoded `PsuedoEOF` character such that
the decoded file was shorter than the original. This resulted from how
the record for the `PsuedoEOF` was written into the file header; it was
always appended as the final record even when it was, e.g., the second-
or third-to-last record. This resulted in some records, including the
`PsuedoEOF`, having incorrect lengths and incorrect encodings when the
header was decoded. Sometimes, this resulted in the decoding being cut
short; in other instances, incorrect symbols were rendered.

Solution is to identify the index of the `PsuedoEOF` record in pairs and
encode that in the header and no longer encode the symbol itself in the
header, removing the need to (i) encode it as two bytes and (ii) place
it at the end to handle it specially. When decoding the header, we skip
the byte whose index is that of `PsuedoEOF`, insert into the pairs list
at the index, and continue as normal.

chore: document `main.zig:{compress * decompress}`

fix: maximum count of codes assigned to length

chore: re-implement decoding test

refactor: extract decoding loop as function

chore: nuked a surviving test

chore: quick documentation

refactor: nuke now-dead code

feat: achieve canonical encoding and decoding

Bug fixing abound!

* Properly skipped the `PsuedoEOF` bytes in
  `xcoding.zig:readHuffmanPairsFromHeader`. Previously, only skipped the
  first byte (`00000001`), shifting the decoding reading frame to the
  left by one byte. Now we skip the second byte too (`00000000`).
* Make `code` in `xcoding.zig:decodedEncodedStream` a `usize` instead of
  a `u8` because, surprise, Huffman codes can be larger than 8 bits.
  Should encode this in an explicit constant.
* Probably others that have been lost to time in the headache that this
  project was.

Also, add and implement the new `compress` and `decompress` functions.
I should decide on what assumptions I want to make on the passed reader
and writer, if any, i.e. if I should make new buffers or take them as
is. Additionally, the code needs a lot of comments, and a lot of
now-dead code has to be removed.

fix: account for header offsets when decoding

fix: write only non-zero lengths

backend implementation of huffman codes