feat: add shell completions for bash and zsh

[njg7194]

Summary

This PR adds shell completion support for both Bash and Zsh.

Changes

• Add Bash completion script (completions/has.bash)
• Add Zsh completion script (completions/_has)
• Update Makefile with install-completions and uninstall-completions targets
• Update README with installation instructions for completions

Usage

After installation, users will get tab-completion for:

• Options (-q, -h, --help, -v, --version, --color-*)
• Command names available on the system

Closes #65

[goto-dev-null]

Love this!

Can createa a separate PR if need be but here's a port of what you did for fish!

completions/has.fish

# Fish completion script for 'has' - https://github.com/kdabir/has
# A simple utility to check the presence of command line tools

# Disable file completions
complete -c has -f

# Options
complete -c has -s q -d 'Silent mode'
complete -c has -s h -l help -d 'Display this help text and quit'
complete -c has -s v -l version -d 'Show version number and quit'
complete -c has -l color-auto -d 'Enable color output automatically (default)'
complete -c has -l color-never -d 'Disable color output'
complete -c has -l color-always -d 'Always enable color output'

# Complete arguments with available commands on the system
complete -c has -f -a '(complete -C (commandline -ct))'

then here are the needed changes to the Makefile

--- Makefile
+++ Makefile
@@ -26,6 +26,7 @@
 # Completion directories
 BASH_COMPLETION_DIR := $(DESTDIR)$(PREFIX)/share/bash-completion/completions
 ZSH_COMPLETION_DIR := $(DESTDIR)$(PREFIX)/share/zsh/site-functions
+FISH_COMPLETION_DIR := $(DESTDIR)$(PREFIX)/share/fish/vendor_completions.d

 # install 'has' in specified directory
 install : has
@@ -37,8 +38,10 @@
 install-completions:
 	mkdir -v -p $(BASH_COMPLETION_DIR) && \
 	mkdir -v -p $(ZSH_COMPLETION_DIR) && \
+ 	mkdir -v -p $(FISH_COMPLETION_DIR) && \
 	cp -v completions/has.bash $(BASH_COMPLETION_DIR)/has && \
-	cp -v completions/_has $(ZSH_COMPLETION_DIR)/_has
+	cp -v completions/_has $(ZSH_COMPLETION_DIR)/_has && \
+	cp -v completions/has.fish $(FISH_COMPLETION_DIR)/has.fish

 # install everything
 install-all: install install-completions
@@ -60,6 +63,7 @@
 uninstall-completions:
 	rm -f $(BASH_COMPLETION_DIR)/has
 	rm -f $(ZSH_COMPLETION_DIR)/_has
+	rm -f $(FISH_COMPLETION_DIR)/has.fish

 uninstall-all: uninstall uninstall-completions