Refactor llw2d.initheight

[tkoskela]

closes #134

• Added parameters for peak position and peak height that were previously hard-coded
• Created a helper function get_initial_height that can be broadcast over the grid. No need for loops.

Master:

@btime Model.LLW2d.initheight!(h, matrices.ocean_depth, params.dx, params.dy, params.source_size);
  4.016 ms (120006 allocations: 10.99 MiB)

This PR

@btime Model.LLW2d.initheight!(h, matrices.ocean_depth, params.dx, params.dy, params.source_size, params.peak_height, params.peak_position);
  237.715 μs (11 allocations: 9.61 KiB)

[giordano]

Nice!!

[giordano]

Just a comment: this can also be done with the hypot function:

Suggested change

	distance_to_peak = sqrt(dx^2 + dy^2)
	distance_to_peak = hypot(dx, dy)

While being more accurate (it doesn't overflow/underflow), hypot is slower than sqrt(...^2 + ...^2 + ...). However for the values of dx and dy we expect, hypot might be an overkill, so in the end this should be fine as it is