Rewrite comment and value update logic
Rewrite comment and value update logic

This both improves readability of the update logic and introduces the ability
to update the value if the value exactly matches the default structured comment
value which is interpreted as the previous Base value. This allows to use the
--default-to-base option with continuous updating values which was not possible
before.

This feature was requested in #4.

Flinesoft/BartyCrouch,Flinesoft/BartyCrouch,Flinesoft/BartyCrouch,Flinesoft/BartyCrouch