New debugging features, cellGame & minor changes

Two cellGame functions partially implemented:
- cellGameGetParamInt
- cellGameGetParamString

New debugging features:
- Call Stack viewer added
- Memory Viewer rewritten (Not finished yet)

Modified definition of UNIMPLEMENTED_FUNC to improve compatibility with
other compilers: Thanks @krofna

Replaced the "Compiler" menu entry with "Tools" and "Memory Viewer"
entry added.

NOTE: To "quickly" browse the memory using the Memory Viewer you can use
the scrollbar. Notice the irony of the word 'quickly' since the memory
viewer is actually slow as fuck. I will fix that soon. As you can see,
I'd like to add a Raw image viewer in the future in order to "see"
textures directly from memory.