Provide Setting duplication mechanism
Add a mechanism to duplicate an existing setting.
Example:
```py
from clickset import Setting
class MyClass:
native = Setting(
'startup.native',
default = True,
option = ClickParams(
'--native/--web',
help = 'Run in a web or native window',
)
)
class OtherClass:
# Copy interface ideas
native = MyClass.native
native = MyClass.native.copy()
native = Setting.copy('startup.native'
# ... below here only used if 'startup.native' doesn't exist
default = True,
option = ClickParams(
'--native/--web',
help = 'Run in a web or native window',
)
)
```
If implemented as `Setting.copy('path.to.setting')`, this could be used to ensure each path has a singleton setting implementation.
issue