Obviously [[parser/keyval.py]] is not installed on this MoinMoin, so I can't give you a live demo.  Here's a mockup, though:

{{{ {{{#!keyval
key1: value1
key2 : value2
key3: value3
This line has no key-value pairs so it doesn't turn into a table

Watch out for colons embedded deep in the line...

They might cause: unexpected results.
} } } }}}

And this looks like:
----
|| key1 || value1 ||
|| key2 || value2 ||
|| key3 || value3 ||
This line has no key-value pairs so it doesn't turn into a table

Watch out for colons embedded deep in the line...

|| They might cause || unexpected results. ||
----

If you need other delimiters besides the colon, you can specify them like this:

{{{ {{{#!keyval delim='='
key1 = value1
key2 = value2
key3 = value3
} } } }}}

which gets you:
----
|| key1 || value1 ||
|| key2 || value2 ||
|| key3 || value3 ||
----

Known problems: embedding wiki-table syntax on a line that gets split can lead to... interesting results :-)

----
default CSV parser does similar :)