Developer release v0.9.4

This is a developer release with minor optimizations and fixes. Some of the more notable changes since v0.9.3 include :

• Add build date to --version output
• Add a missing trailing slash that was causing resource-loading to fail
• Stop using unportable RTLD_DEFAULT
• Remove little-used assert()
• (Prematurely) optimise sparseram
• Drop ancient 24-bit address space stricture
• Remove obsolescent SPI simulated device
• Make emscripten build a first-class citizen (make PLATFORM=emscripten)
• Improve Javascript (emscripten build) code style and optimisability
• Remove obsoleted conditional code for emscripten
• Make clang compilation use clang++
• Support disassembly in emscripten build