Pyhmmer

Changed
- Allow `AlphabetMismatch` error to allow for an unknown *actual* alphabet.
- Make `HMMFile` and `HMMPressedFile` raise `AlphabetMismatch` on files with mixed alphabets.

Fixed
- Avoid calling `fclose` with null pointers in `Sequence.write` and `MSA.write`.

Fixed
- `HMM.__setstate__` not properly extracting the cutoff from `pickle` state for some HMMs ([67](https://github.com/althonos/pyhmmer/issues/67)).

Changed
- Update and remove some test files to reduce size of distributed package data.

Fixed
- Compilation of Easel and HMMER code not using SSE4.1 extensions.

Fixed
- Implement `write` function for `fopencookie` with `off_t` instead of `off64_t` for compatibility.
- Fix handling of NULL buffers passed to `read` and `write` methods of `fopencookie`.

Fixed
- Reallocation issue causing segmentation faults in `nhmmer` with more than 64 sequences ([62](https://github.com/althonos/pyhmmer/issues/62)).

Added
- Getter to access the strand of a `Domain` produced by a `LongTargetsPipeline`.

Changed
- Display model and cutoff names in `MissingCutoffs` error message, if any.
- Allow `LongTargetsPipeline` to be configured with window length and beta parameters.
- Make `nhmmer` use the window length and beta from the options when creating a `Builder`.

Fixed
- `nhmmer` not computing E-values for non-default window lengths ([moshi4/pybarrnap2](https://github.com/moshi4/pybarrnap/issues/2)).
- `SequenceFile` and `MSAFile` crashing with a segmentation fault when given the path to a folder rather than a file.