PDFiumSharp

Fix for out of range exception on page insert. It was possible to call Insert/Add without the _pages List being initialized, some methods checked this, others didn't. I moved the initialization to the constructor.

Add CallingConvention.Cdecl to file read and write handler delegates (x86). Allow count=0 in FromStream to calculate stream length.

[FIX] ObjectDisposedExceptions are now properly thrown when trying to access disposed PDFium objects

Merge branch 'master' of https://github.com/ArgusMagnus/PDFiumSharp

Updated copyright/license file headers