Only try to remove ltmain.sh if it exists
First stab at consting public functions

This is all the changes that _don't_ provoke compiler warnings from existing
code about implicit casting.

It also includes a fix for regen-prototypes.pl so it parses prototypes with
const in them correctly.
Remove consts that -Wall warned me about
Create struct all at once rather than initializing each member separately
Add more const to MMDB_open filename parameter
Small formatting fix
Update docs for const changes
Mention const additions in Changes.md
Merge pull request #16 from maxmind/dave/const-public-functions

Dave/const public functions