Export sandbox/ headers

These are needed to launch on Windows.
Include chromiumcontent.dll's import library
Rename dist/include to dist/src

This is in preparation for including non-header files in this directory.
Export content/app/startup_helper_win.cc to clients

This is needed to build executables on Windows.
Create and export sandbox_static.lib for Windows clients

sandbox.lib isn't usable out of the box because it expects base's
symbols to be decorated with __declspec(dllexport). So we create a copy
of it that expects them to be decorated with __declspec(dllimport),
as they will be when used in a client application.
Export base_static.lib for Windows clients
Fix exporting of WebKit symbols

We had a duplicate target_definitions dictionary.
Generate libchromiumcontent-symbols.zip on Windows

PDB files required for building go into libchromiumcontent.zip. PDB
files only required for debugging go into
libchromiumcontent-symbols.zip.
Use the DLL version of the CRT

This is required so embedding apps can pass types like std::string into
chromiumcontent.dll.

The DLL CRT seems to require exceptions to be enabled. This matches what
Chromium does for component builds.
Export libGLESv2.dll on Windows
Export icudt.dll for Windows clients
Merge pull request #12 from brightray/windows-brightray_example

Changes needed for building brightray_example on Windows