Clarify BITLIST format and include an example.

This specifies the format of the ultimate value. It should be followed

by a colon and one of the strings B<ASCII>, B<UTF8>, B<HEX> or B<BITLIST>.

If no format specifier is included then B<ASCII> is used. If B<UTF8> is specified

then the value string must be a valid B<UTF8> string. For B<HEX> the output must

be a set of hex digits. B<BITLIST> (which is only valid for a BIT STRING) is a

comma separated list of set bits.

If no format specifier is included then B<ASCII> is used. If B<UTF8> is

specified then the value string must be a valid B<UTF8> string. For B<HEX> the

output must be a set of hex digits. B<BITLIST> (which is only valid for a BIT

STRING) is a comma separated list of the indices of the set bits, all other

bits are zero.

=back

 EXPLICIT:0A,IA5STRING:Hello World

A BITSTRING with bits 1 and 5 set and all others zero:

 FORMAT=BITLIST,BITSTRING:1,5

A more complex example using a config file to produce a

SEQUENCE consiting of a BOOL an OID and a UTF8String: