Clarify dmd prerequisite in README

Must use the installer version, not the zip
Remove default port

Removed the default value for port. May help a reported issue, also
makes the perf code that skips executing queries if the connection
string hasn't been set by a human more simple.
Ensure proper permissions

Ran into an issue whereby libcurl.dll had no xwr permissions for anybody
which in turn prevented the dll from loading into unittests and presented
what would be an otherwise obscure failure for anyone unfamiliar with this
symptom.

Added a chmod line as this should do no harm but kill the potential for this
strange error. Sudo was not necessary on my system.
Fix function signatures

Changed from void* types to type-aware handle types for the few
functions I forgot to fix earlier. Also added with statements
to several functions for future development.