start to add new customizable function for add custom delmiters.

Added "block_distance_custom", "cosine_custom"

compare results:

select stringmetrics("block_distance","phrase","via giuseppe-garibaldi","via giuseppe garibaldi",NULL);
--> Cosine Similarity between "via giuseppe-garibaldi" & "via giuseppe garibaldi" is "0.408248" and yields a  41% similarity

select stringmetrics("block_distance_custom","phrase","via giuseppe-garibaldi","via giuseppe garibaldi","-");
--> Block Distance customized between "via giuseppe,garibaldi" & "via giuseppe garibaldi" is "0" and yields a 100% similarity.

Signed-off-by: aperi2007 <aperi2007@gmail.com>