chasquid-util: Remove dependency on docopt-go

The docopt-go library is quite convenient, but it has been abandoned for
a while :(

Since we only use it for chasquid-util, this patch removes it and
replaces it with a custom small parser, that is a reasonable fit for the
required use cases.

The patch also adds a couple of tests to increase coverage.

NOTE: docopt-go accepted some undocumented behaviour, in particular the
use of "-a b" instead of "-a=b". The new parser does not, so some
user scripts may require updating.

I think this should be rare enough not to be worth the complexity of
adjusting the parser to allow it.

cmd/chasquid-util/test.sh

@@ -8,7 +8,7 @@ init
 go build || exit 1
 
 function r() {
-	./chasquid-util -C .config "$@"
+	./chasquid-util -C=.config "$@"
 }
 
 function check_userdb() {
@@ -44,6 +44,22 @@ if r authenticate user@domain --password=abcd > /dev/null; then
 	exit 1
 fi
 
+# Interactive authentication.
+# Need to wrap the execution under "script" since the interaction requires an
+# actual TTY, and that's a fairly portable way to do that.
+if hash script 2>/dev/null; then
+	if ! (echo passwd; echo passwd ) \
+		| script \
+			-qfec "./chasquid-util -C=.config authenticate user@domain" \
+			".script-out" \
+		| grep -q "Authentication succeeded";
+	then
+		echo interactive authenticate failed
+		exit 1
+	fi
+fi
+
+
 if ! r user-remove user@domain > /dev/null; then
 	echo user-remove failed
 	exit 1
@@ -99,4 +115,9 @@ if r aliases-add alias3@notexist target > /dev/null; then
 	exit 1
 fi
 
+if r aliases-add alias4@domain > /dev/null; then
+	echo aliases-add without target worked
+	exit 1
+fi
+
 success