Instead of providing a function for each entry-type, use a small
static lookup-table and one function to rule them all.
In the future, in case the list grows, we might think about
implementing it with a small hash-lookup, but currently,
it's easy enough synchronizing the enum and the array.
While at it, improve the logic in the code itself
by using logical OR's instead of AND's.
On each request send "last-modified" header with the modification time of
each file. the client will store this field and send it on the next
request(s). On the server check the "if-modified-since" field with the
modified date sent by the client, depending on this send all the data or
the "304 not modified" http status.
CAVEAT: it is assumed the exact field will be send by the client, no date/time
conversion is done for simplicity sake, as far as that's possible with http ;)
