Add keyword classes and keys.list/describe services

[mikelangmayr]

• add Keyword class to libby
• add keyword types (bool, int, float, string, trigger)
• update README

[prkrtg]

I think this makes it

        FloatKeyword(f"positionvalue{s}",
                     getter=lambda: self.controller.get_pos(self.device_key, self.axis),
                     setter=self._set_position,
                     validator=self._check_soft_limits,
                     units=self.units,
                     description="Stage position in engineering units."),

What about making a builder object?

from libby import (
    FloatKeyword
)

class KeywordBuilder:
    def __init__(self, daemon):
        self._daemon = daemon
        self._keywords = []

    def _add(self, kw):
        self._keywords.append(kw)
        return kw

    def float(self, name, *, get=None, set=None, units=None,
              description="", nullable=False, validator=None):
        return self._add(
            FloatKeyword(
                name,
                getter=get,
                setter=set,
                units=units,
                description=description,
                nullable=nullable,
                validator=validator,
            )
        )

Then in Hispec

class HispecDaemon:
    def __init__(self):
        self.keywords = KeywordBuilder(self)

def on_start(self, _libby):
    self.keywords.float(
        "position",
        get=lambda: self.controller.get_pos(...),
        set=self._set_position,
        units="mm",
        description="Stage position",
    )