Vis version 0.7

This is mostly a bug fix release with fixes for a few cases of undefined behavior and preliminary work for experimentation with different core text management data structures and general editor architecture.

• fix UB in core text management data structure
• text refactoring, splitting out reusable text iterator and I/O components
• new *at() variants taking directory descriptor for file load/save API
• more efficient initial file read, avoiding spurious syscalls and copy
• text API cleanups, const correctness improvements
• increased test coverage for core text data structure
• support for Lua 5.4
• Lua API improvements: vis.mark, vis.register, vis.win.file.modified
  and support for terminal CSI events
• NetBSD support
• new :set ignorecase option to search case independently
• new visual mode mapping <C-a> to select all matching selections
• fix mappings involving non-leading <C-c>
• minor file detection fixes for racket, node.js modules, Typescript and liliypond
• new lexers for Zig, meson build system, Mikrotik RouterOS scripts, Gemini
• improved inner word text object and its use for <C-n> in normal mode
• improved <C-n> behavior in visual mode
• removed ie, ae inner/outer entire text object, use :, as shorthand for :0,$
• removed pairwise selection combinators z>, z<, z-, z+, z&, z|
• remove ~ as alias for g~
• use ~ instead of ! for selection complement
• remove special key and window related aliases
• vis-open(1) adds a trailing slash to indicate folders
• add primary clipboard support to vis-clipboard(1)
• support wayland clipboard using wl-clipboard(1)
• new Makefile targets: distclean, testclean