Rename DLLEXPORT AND STDCALL

This CL renames DLLEXPORT to FPDF_EXPORT and STDCALL to FPDF_CALLCONV to
be more PDFium specific.

This is split off of https://pdfium-review.googlesource.com/c/8970 by
Felix Kauselmann.

Bug: pdfium:825
Change-Id: I0aea9d43f1714b1e10e935c4a7eea685a5ad8998
Reviewed-on: https://pdfium-review.googlesource.com/10610
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>
diff --git a/AUTHORS b/AUTHORS
index 9b63c71..8e17b65 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -15,6 +15,7 @@
 Chery Cherian <cherycherian@gmail.com>
 Chris Palmer <palmer@chromium.org>
 Dan Sinclair <dsinclair@chromium.org>
+Felix Kauselmann <licorn@gmail.com>
 Finnur Thorarinsson <finnur@chromium.org>
 GiWan Go <gogil@stealien.com>
 Jiang Jiang <jiangj@opera.com>