Add lint rule for "if-begin" (rather than using `cond')

Print all warnings for multiple issues of same type on same line

Improve quoted constant detection

Avoid warnings for problems originating outside the current source file

Allow chicken-install flags to be passed to load-system

Use "rev" variable in Niv example

Allow chicken-lock output to be redirected with "-output-file" flag

Drop unnecessary minimum dependency versions in egg file

Allow chicken-install to try remote sources if not found in local paths

Expose beaker egg via Nix attribute

Make egg-file argument to load-system optional

Allow passing specific paths to chicken-clean

More flake documentation

Add flake example to documentation

Add Nix helpers to flake

Small documentation updates for Nix helpers

Add gitignore file

Avoid file collisions among eggPrograms that use the same eggs

Add example chicken-lock commands to Nix helper documentation

Add examples of linking to external libraries with Nix helpers