Line fitting fails for two data points

[mgely]

The following code fails

from oitg.fitting import line
line.fit([0,1],[0,1])

with error

Traceback (most recent call last):
  File "C:\Users\LocalAdmin\Miniconda3\envs\artiq-env\lib\site-packages\oitg-0.1-py3.9.egg\oitg\fitting\FitBase.py", line 249, in fit
  File "C:\Users\LocalAdmin\Miniconda3\envs\artiq-env\lib\site-packages\scipy\optimize\minpack.py", line 795, in curve_fit
    res = least_squares(func, p0, jac=jac, bounds=bounds, method=method,
  File "C:\Users\LocalAdmin\Miniconda3\envs\artiq-env\lib\site-packages\scipy\optimize\_lsq\least_squares.py", line 805, in least_squares
    raise ValueError("`x0` is infeasible.")
ValueError: `x0` is infeasible.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "y:/testing/scratch_mfg/line_fit.py", line 2, in <module>
    line.fit([0,1],[0,1])
  File "C:\Users\LocalAdmin\Miniconda3\envs\artiq-env\lib\site-packages\oitg-0.1-py3.9.egg\oitg\fitting\FitBase.py", line 255, in fit
oitg.fitting.FitBase.FitError: `x0` is infeasible.

One obvious thing that would fail is the parameter_initialiser in line.py

oitg/oitg/fitting/line.py

Lines 6 to 9 in 9b64b4e

	def parameter_initialiser(x, y, p):
	k = (y[-1] - y[1]) / (x[-1] - x[1])
	p['a'] = y[1] - x[1] * k
	p['b'] = k

which would give division by 0 errors for a size two array.