These two methods were not well-thought. While a control that has the
read-only flag set is certainly not writeable, a control with the
write-only flag set could still be unwriteable because of being inactive.

The original intention for these two methods was to check for the flags,
so adjust their behaviour and naming accordingly.

Before 000696e, a control was assumed (and reported by this method) to be
writeable when the read-only was not set. However, such a control would
still be unwriteable when being flagged as inactive, which was not taken
into account before.

In other words, is_writeable now checks that a control can *actually* be
written to.

This will be used later to facilitate instantiation of a Controls object with diverse Control sub-classes.

…oved into a method of class Control

…PEP8

This commit covers the part up to LegacyControl, as discussed in #15.
The upgrade path for existing code is:

Use LegacyControl instead of Control for instantiations, and use either
BaseControl or BaseSingleControl for isinstance() checks (see Controls).

See #15 (comment) .

is_<flag> is working for many of the flags, but is weird for stuff like
V4L2_CTRL_FLAG_HAS_PAYLOAD or V4L2_CTRL_FLAG_UPDATE. Switching to
is_flagged_<flag> to check if a flag is set, e.g. is_flagged_has_payload,
is still not perfect, but better.

…ntrol's __repr__, too

…l doesn't have the attributes minimum and maximum.

…hich is used by default.

…tiation of different control class objects without a messy if/elif construct.

…m optional (default: on)

…efore trying to mangle it

…trol

This class inherits from UserDict and thus can be used like a dict to access
the items defined for the menu. For the sake of this dict-like behaviour the
MenuItem class is not used in MenuControl; the names of the menu items will
be transformed straight to either string or integer, depending on the menu
type.

MenuItem is kept for now, but renamed to LegacyMenuItem to signal it should
not be used except for legacy code.

…umeric controls

This will most probably be the last patch in the current series of the
improve_controls branch for now. This series closes #15 and closes #12.

…egacyControl for control types not found in ctrl_type_map.

the rest to the new derived class BaseMonoControl. The latter is more
or less a reprise of BaseSingleControl, which had been removed in
5640d4e. It's similar but not identical, and used to prepare for the
upcoming ButtonControl.

no real device that provides a button control and trying vivid did
not work (see #17).

is named opencv-python; call pip as module, as suggested in the pip
manual. Closes #22.