OpenSystemsDevelopment / qpdf

This improves indentation of long strings. This commit also fixes some
trailing whitespace in ChangeLog.

Having it at compile time breaks cross-compilation and isn't really
right anyway.

Run this:

for i in  **/*.cc **/*.c **/*.h **/*.hh; do
  clang-format < $i >| $i.new && mv $i.new $i
done

Fix is based on guidance
https://support.microsoft.com/en-us/help/238187/cryptacquirecontext-use-and-troubleshooting
and is the proper fix for #285/#286

Thanks to github user zdenop for supplying some additional
error-handling code.

This makes all integer type conversions that have potential data loss
explicit with calls that do range checks and raise an exception. After
this commit, qpdf builds with no warnings when -Wsign-conversion
-Wconversion is used with gcc or clang or when -W3 -Wd4800 is used
with MSVC. This significantly reduces the likelihood of potential
crashes from bogus integer values.

There are some parts of the code that take int when they should take
size_t or an offset. Such places would make qpdf not support files
with more than 2^31 of something that usually wouldn't be so large. In
the event that such a file shows up and is valid, at least qpdf would
raise an error in the right spot so the issue could be legitimately
addressed rather than failing in some weird way because of a silent
overflow condition.

Most of the README files have been renamed. Refer to the new names.

For cross compiling.

As reported in issue #40, a call to CryptAcquireContext in
SecureRandomDataProvider fails in a fresh windows install prior to any
user keys being created in AppData\Roaming\Microsoft\Crypto\RSA.

Thanks michalrames.

Add new RandomDataProvider object and implement existing random number
generation in terms of that.  This enables end users to supply their
own random data providers.