Unicycler v0.4.4

A small release with a few bug fixes:

• Makefile fix for GCC 7 (thanks @cerebis!)
• Fixed crash when using contamination filter (thanks @phbrito!)
• Fixed a bug leading to unnecessarily slow path finding in hybrid assemblies
• Fixed some bugs related to dead-end trimming in hybrid assemblies
• Fixed an off-by-one error in contig placement into miniasm assemblies

and one new feature:

• Added --existing_long_read_assembly option. Allows a high quality long-read assembly (e.g. from Nanopolish or Arrow) to be injected into Unicycler's hybrid assembly pipeline. Can improve final assembly accuracy when short reads have incomplete coverage.