fix initialization order, unused var, make cleanup

[svenevs]

• Fixes initialization order in tinyply.h
• Comments out an unused auto result in tinyply.cpp
• Makefile improvements
  • Add -Wall and -Wpedantic (what catches the initialization order warnings)
  • Add a clean target
  • Add tinyply.{h,cpp} to the dependency list of tinyply-core executable so that updates to those files trigger a new build

[ddiakopoulos]

thanks!