fs(3lua): init man pages

Initialise man pages for the fs module.

man/fs/fs.dirname.3lua.scd

@@ -0,0 +1,30 @@
+FS.DIRNAME(3lua) "3lua" "Callisto manual pages"
+
+# NAME
+*fs.dirname* - get the parent directory of a path
+
+# SYNOPSIS
+*fs.dirname*(_path_: *string*)
+
+# DESCRIPTION
+*fs.dirname* returns the parent directory of _path_.
+
+Any trailing "/" characters found in _path_
+are not counted as part of the directory name.
+If _path_ is an empty string or contains no "/" characters,
+the string "." is returned.
+
+This is purely a string manipulation function
+and depends on no outside state.
+
+# EXAMPLES
+Print the directory containing the current script file:
+
+	print(fs.dirname(arg[0]))
+
+Output example:
+
+	assert(fs.dirname("/usr/local/bin") == "/usr/local")
+
+# SEE ALSO
+callisto(3lua), fs(3lua)