I simplified a lot of API calls by pulling panel memory management
inside the library. All API calls which previously required a panel
as parameter are now handling their panel themself.
Nuklear now has three different property versions for int, float and
added by this commit a double version. Internally an additional change
happend. Now the type of the property is actually taken into account
and floating pointer errors due to casting are less of an issue.
Previously I packed standard library variable arguments as well as
file operation into one define `NK_INCLUDE_STANDARD_IO`. This caused
some problems and I split the define into two. So if you want the old
behavior you need to define `NK_INCLUDE_STANDARD_IO` as well as
`NK_INCLUDE_STANDARD_VARARGS`. If you only want file operations but
not variable arguments only define `NK_INCLUDE_STANDARD_IO` and
if you only want varargs but not file operations please only define
`NK_INCLUDE_STANDARD_VARARGS`.
