slow5tools-v0.4.0

• multithreaded support for slow5tools split
• performance improvements to sequential reading in slow5tools merge, view etc.
• --retain option added to f2s (#53)
• improve support in f2s for older fast5 files [#54]
• improvements to real-time fast5 to slow5 conversion script
• catch and gracefully error out when slow5tools sees FAST5 end_reason corrupted with ONT's compress_fast5 programme (#59)
• improved error handling, better error messages and warnings
• more documentation added: mainly suggestions for archiving