The new code you updated works great but if I leave the timer functions in the cpp then it won't compile. 
I get this in the IDE
...\Arduino\libraries\NewPing\NewPing.cpp: In static member function 'static void NewPing::timer_us(unsigned int, void (*)())':
...\Arduino\libraries\NewPing\NewPing.cpp:151: error: 'OCR2A' was not declared in this scope
...\Arduino\libraries\NewPing\NewPing.cpp:152: error: 'TIMSK2' was not declared in this scope
...\Arduino\libraries\NewPing\NewPing.cpp:152: error: 'OCIE2A' was not declared in this scope
...\Arduino\libraries\NewPing\NewPing.cpp: In static member function 'static void NewPing::timer_ms(long unsigned int, void (*)())':
...\Arduino\libraries\NewPing\NewPing.cpp:167: error: 'OCR2A' was not declared in this scope
...\Arduino\libraries\NewPing\NewPing.cpp:168: error: 'TIMSK2' was not declared in this scope
...\Arduino\libraries\NewPing\NewPing.cpp:168: error: 'OCIE2A' was not declared in this scope
...\Arduino\libraries\NewPing\NewPing.cpp: In static member function 'static void NewPing::timer_stop()':
...\Arduino\libraries\NewPing\NewPing.cpp:177: error: 'TIMSK2' was not declared in this scope
...\Arduino\libraries\NewPing\NewPing.cpp:177: error: 'OCIE2A' was not declared in this scope
...\Arduino\libraries\NewPing\NewPing.cpp: In static member function 'static void NewPing::timer_setup()':
...\Arduino\libraries\NewPing\NewPing.cpp:195: error: 'ASSR' was not declared in this scope
...\Arduino\libraries\NewPing\NewPing.cpp:195: error: 'AS2' was not declared in this scope
...\Arduino\libraries\NewPing\NewPing.cpp:196: error: 'TCCR2A' was not declared in this scope
...\Arduino\libraries\NewPing\NewPing.cpp:196: error: 'WGM21' was not declared in this scope
...\Arduino\libraries\NewPing\NewPing.cpp:197: error: 'TCCR2B' was not declared in this scope
...\Arduino\libraries\NewPing\NewPing.cpp:197: error: 'CS22' was not declared in this scope
...\Arduino\libraries\NewPing\NewPing.cpp:198: error: 'TCNT2' was not declared in this scope