Fix leaks in MMDB_open()

If obtaining the database size fails free the allocated memory and close
the file descriptor.
Merge pull request #49 from fgsch/master

Fix leaks in MMDB_open()
Added note about leak fix to Changes.md
Correct example
Merge pull request #50 from fgsch/master

Correct example
Added change for documentation fix
Visual Studio build files and Windows fixes

# HG changeset patch
# User Stone Steps <support@stonesteps.ca>
# Date 1415592468 18000
#      Sun Nov 09 23:07:48 2014 -0500
# Node ID b1c3a26e9fdb76a0c466ec458f2bb12adea60d55
# Parent  0a7fe7dfadeccbfad338ad1221d8aaf9e64783b6
Source patch

Signed-off-by: Gregory Oschwald <goschwald@maxmind.com>