build: add dune project skeleton and library stanza

The meow library against unix, plus ignore rules for _build, generated
sources and the meowc symlink.

.gitignore

@@ -0,0 +1,12 @@
+_build/
+build/
+gen/
+out/
+meowc
+*.install
+compile_commands.json
+examples/raytracer/include/rt_config.h
+*~
+\#*\#
+.\#*
+.cache/

dune-project

@@ -0,0 +1,2 @@
+(lang dune 3.0)
+(name meowc)

lib/dune

@@ -0,0 +1,3 @@
+(library
+ (name meow)
+ (libraries unix))