v1.5.3: 2021 release

Consider this more of a bugfix/stability release, with most features originating from the first three months of 2021. Featuring:

• removing obsolete generate_report
• xlt (1f85176)
• xge, xle optimized
• xge
• multiline constpp macros
• many new instructions implemented for bfvm
• a new ucode compiler.
• bugfixes to bfadbg (more edge-case handling in edit mode)
• improved compatibility with weird systems
• lbl imm optimization
• bfdata and bflabel performance improvements
• SK calculus evaluator example
• vxcall patch; bfdata addressing bugfixes.
• merged vxcall and constpp, bfdata and bflabels.
• sle now works correctly on an empty stack
• multiple bfvm bugfixes
• bfmake no longer requires -b to go along -c.
• bfvm output is more portable
• inline brainfuck is now supported by bfvm (although it's not optimized yet).
• linear-bounded automata optimizer in Java (remotely useful for asm2bf programs).