Include "apply" function in the fluent API

I've been modelling something with a lot of angle-iron sections. I've got a little fed up with writing lots of bits like:

```python
myobj = (myobj
.faces('>X')
.workplane()
.moveTo(corner_x, corner_y)
.hLine(angle_size).vLine(-angle_thickness)
.hLine(-(angle_size-angle_thickness)).vLine(-(angle_size-angle_thickness))
.hLine(-angle_thickness).vLine(angle_size)
.close()
.extrude(angle_length)
)
```

and it occurred to me it would be really useful if there was a way to define a function so that the code could look like this:

```python
def draw_angle_profile(obj, angle_size, angle_thickness, orientation):
if orientation == 'southeast':
return (obj
.hLine(angle_size).vLine(-angle_thickness)
.hLine(-(angle_size-angle_thickness)).vLine(-(angle_size-angle_thickness))
.hLine(-angle_thickness).vLine(angle_size)
.close()
)

# elsewhere...

myobj = (myobj
.faces('>X')
.workplane()
.moveTo(corner_x, corner_y)
.apply(draw_angle_profile, angle_size, angle_thickness, 'southeast')
.extrude(angle_length)
)

```

I know I could do this by breaking the flow, something like this:

```python
myobj = (myobj
.faces('>X')
.workplane()
.moveTo(corner_x, corner_y)
)
myobj = (draw_angle_profile(myobj, angle_size, angle_thickness, 'southeast')
.close()
.extrude(angle_length)
)
```

but having an `apply` function seems a bit cleaner than leaving the string of functions with a last `moveTo`, then having to start a new set of functions. Not the biggest issue in the world, I'll grant you, but it would presumably be very easy to implement...