add pkg-config support
packaging: remove the --with-pkgconfigdir option

It was not necessary and would only confuse packagers.
packaging: fixup pkg-config

Set the private libs as determined by configure, and add the missing lib link.
packaging: add pkg-config file to gitignore
Merge pull request #18

4212f7d packaging: add pkg-config file to gitignore (Cory Fields)
67a4765 packaging: fixup pkg-config (Cory Fields)
81b2fae packaging: remove the --with-pkgconfigdir option (Cory Fields)
c7ee71f add pkg-config support (Amir Taaki)