v0.3.4

This release includes a new method called read_record_set_exact(), which allows
specifying the number of records that should be present in a record set.
This feature is required for parallel processing of paired-end reads
(see also here).
Thanks @nh13 for the contribution
to this feature.

More changes:

• Added buf_capacity and shrink_buffer_to_fit to fasta::RecordSet and
  fastq::RecordSet, allowing more control over the buffer size.