Add function to expand ~ in .stowrc files (#14)

Add a new expand_tilde() function that performs tilde expansion of
strings, and corresponding unit tests:

    * A ~ at the beginning of a path is expanded to the user's home
      directory.
    * Literal '~' can be provided with '\~'

Combine this with expand_environment() in a new expand_filepath()
function which applies all (both) required expansion functions to a
string, and use that in get_config_file_options() to expand .stowrc
options.

Add more tests to check that tilde expanded in correct places, i.e.:

    * expanded for --target and --dir
    * not expanded for --ignore, --defer, or --override

Update documentation on stowrc files according to this functionality
change.

Fixes #14: https://github.com/aspiers/stow/issues/14

t/rc_options.t

@@ -7,7 +7,7 @@
 use strict;
 use warnings;
 
-use Test::More tests => 15;
+use Test::More tests => 23;
 
 use testutil;
 
@@ -107,6 +107,16 @@ delete $ENV{'WITH_UNDERSCORE'};
 # Expansion with escaped $
 is(expand_environment('\$HOME/stow'), '$HOME/stow', 'expand \$HOME');
 
+#
+# Test tilde (~) expansion
+#
+# Basic expansion
+is(expand_tilde('~/path'), "$ENV{HOME}/path", 'tilde expansion to $HOME');
+# Should not expand if middle of path
+is(expand_tilde('/path/~/here'), '/path/~/here', 'middle ~ not expanded');
+# Test escaped ~
+is(expand_tilde('\~/path'), '~/path', 'escaped tilde');
+
 #
 # Test that environment variable expansion is applied.
 #
@@ -130,6 +140,29 @@ is_deeply($options->{defer}, [qr(\A\$HOME)],
 is_deeply($options->{override}, [qr(\A\$HOME)],
     "environment expansion not applied on --override");
 
+#
+# Test that tilde expansion is applied in correct places.
+#
+$rc_contents = <<'HERE';
+--dir=~/stow
+--target=~/stow
+--ignore=~/stow
+--defer=~/stow
+--override=~/stow
+HERE
+make_file($RC_FILE, $rc_contents);
+($options, $pkgs_to_delete, $pkgs_to_stow) = get_config_file_options();
+is($options->{dir}, "$OUT_DIR/stow",
+    "apply environment expansion on stowrc --dir");
+is($options->{target}, "$OUT_DIR/stow",
+    "apply environment expansion on stowrc --target");
+is_deeply($options->{ignore}, [qr(~/stow\z)],
+    "environment expansion not applied on --ignore");
+is_deeply($options->{defer}, [qr(\A~/stow)],
+    "environment expansion not applied on --defer");
+is_deeply($options->{override}, [qr(\A~/stow)],
+    "environment expansion not applied on --override");
+
 # Clean up files used for testing.
 #
 unlink $RC_FILE or die "Unable to clean up $RC_FILE.\n";