Release 0.20.1

Tool

• Initial file load in the GUI is now near-instant thanks to a refactor in how headers are loaded.
• non-mmaped processing now operates at a reasonable speed.

Library

• rewrite bio (non-mmap) backend stuff to use a bytearray buffer loaded at init instead of repeated seek()->read() calls.
• non-mmap now automatically kicks in if mmap fails
• GUI now supports a target-function-based lazy loading string buffer, which is used for header lazy-loading