dsc v0.8.5

This version of dsc offers a few bug fixes, and adds a new optimization pass: -felide-runtime-casts, which tries to elide redundant runtime casts. The new optimization is activated at the -O2 optimization level, as well as any higher optimization levels.

Furthermore, the SSA optimization passes will now try to promote arguments to SSA variables, and then recycle the argument variables during the SSA deconstruction process. This should improve codegen in some cases, as it enables the compiler to apply the normal SSA-based scalar optimizations to argument variables.