Blank line removal
Replaced nested clock_allocator class logic with new simple_allocator class template specialisation
Minor formatting change
Added peripheral_in_use exception class
Moved supporting clock types - frequency et al, fixed_oscillator_clock_source, clock_source, clock_filter, clock_frequency to their own header file clockdefs.h
Comment change
Added any_in_use query member function
WIP: added initial workings of internal PWM control type pwm_ctrl