Improve resolution of paths for DECLARE LIBRARY

[QB64Bot]

Issue by flukiluke Monday Oct 29, 2018 at 13:58 GMT Originally opened as https://github.com/Galleondragon/qb64/issues/71

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The current logic used is very sucky:

• Code includes must use a .h extension
• Dynamic libraries must begin with lib on Linux
• The appropriate places aren't searched for dynamic libraries, causing machine-specific constants needing to be hard coded in
• Probably other problems