Æsthetic improvements and two fixes

[Porges]

Fixes: #26, also returns once we hit an error in the loop instead of continuing.

(Mostly) stylistic changes:

• Remove a few unneeded buffers and variables
• sprintf → sprintf_s
• Simplify DWORD extraction code (this needs review – is it possible to store non-DWORD data in DWORD entries like you can shove anything into REG_SZ?)
• Use nullptr
• Junk TCHAR and its ilk

Needed:

• Need to add a test for dodgy non-null-terminated data, but I'm not sure the best way to actually get this into the registry in the first place, since REG.EXE is going to do it correctly. Can we add adjunct C++ programs to the test code somehow?

[shiftkey]

Can we add adjunct C++ programs to the test code somehow?

If there's a test harness that's easy enough to setup and run from tasks in package.json (I'm happy to help write the shell scripts for this) then let's get this stuff in.

EDIT: moving this to #28

[shiftkey]

Code looks good. Just a tweak to the code comments in the other places where we're formatting errors.

making the changed myself

[shiftkey]