Adapts to current sdkman; improvements.

- All commands now don't tab-complete after the maximum
   number of parameters.
 - Specifies aliases in a more compact way.
 - Adds commands update, upgrade.
 - Removes some dead code.

Fixes issues #1, #2, #5

conf.d/sdk.fish

@@ -0,0 +1,11 @@
+#!/usr/bin/fish
+
+# sdk command
+function sdk
+    bash -c "source $HOME/.sdkman/bin/sdkman-init.sh && sdk $argv"
+end
+
+# add paths
+for ITEM in $HOME/.sdkman/candidates/* ;
+    set -gx PATH $PATH $ITEM/current/bin
+end