Bump to version 0.4.0.

Bump to version 0.4.0.
Add multiple-inclusion protection.
Add new function to write masked bits to PCI config space. This mirrors
    functionality currently available in X.org that is slated to be
    removed.
Gut old regex based search mechanism with a new mechanism that is modeled
    after the Linux kernel. In addition to searching for devices by device
    / vendor ID, it is possible to search for devices by their domain / bus
    / slot / function.
Fix serious bus in the reading of ROMs and in the unmapping of regions. The
    main point is that the map routine depens on the pci_mem_region::memory
    pointer being non-NULL only when the region is mapped. Therefore, the
    unmap routine should set it to NULL after unmapping.
Update to use new search API.