src: brightness: Fix LOG_BRIGHTNESS == 1

Various includes where missing, making the compilation with LOG_BRIGHTNESS
enabled fail.
src: Replace functions dealing with string conversions with <stdio.h> equivalents

This replaces all occurences of the custom string conversion function with the
printf() and scanf() function family. Although this takes up considerable
amount of space, it is more flexible and the advanced features of these
functions can come in handy in this project.
src: Implement module specifying format strings

This introduces a new module, which specifies various format strings and makes
them accessible througout the whole project. These strings are put into program
space once and can be re-used across different other modules.

On top of that this commit makes also sure that all of the existing printf()
invocations make use of this new facility.
src: Remove unused base includes
src: config.h: LOG_LDR2PWM: Add todo items
Merge branch 'feat/printf'