fs(3lua): init man pages

Initialise man pages for the fs module.

man/fs/fs.copy.3lua.scd

@@ -0,0 +1,44 @@
+FS.COPY(3lua) "3lua" "Callisto manual pages"
+
+# NAME
+*fs.copy* - copy a file
+
+# SYNOPSIS
+*fs.copy*(_source_: *string*, _target_: *string*)
+
+# DESCRIPTION
+*fs.copy* copies the contents of the _source_ file to the _target_ file,
+overwriting any existing contents of the _target_ file.
+
+It can be considered analogous to the *cp* shell command.
+
+The call _fs.copy("src", "trg")_ is roughly equivalent to the following
+Lua code:
+
+```
+local sf, se = assert(io.open("src", 'r'))
+local tf, te = assert(io.open("trg", 'w'))
+
+repeat
+	local readbuf = readbuf or ""
+	tf:write(readbuf)
+	readbuf = sf:read(512)
+until not readbuf
+```
+
+# EXAMPLES
+Create a file _tel_ and write some data to it,
+and copy its contents to the file _tel2_:
+
+```
+local contents = [[
+maja    0501-1136285
+peter   0136-7399214
+]]
+io.output("tel"):write(contents)
+fs.copy("tel", "tel2")
+assert(io.input("tel2"):read("a") == contents)
+```
+
+# SEE ALSO
+callisto(3lua), fs(3lua), fs.move(3lua)