Histogram title customization

[adeak]

I noticed that the histogram title always looks something like this:

Speaking of pedantic, I find "speed" with units of time surprising :) Beyond pedantry I would expect "larger speed" meaning faster, while "larger time interval" meaning slower.

Looking at the implementation the "Speed in" prefix seems hard-coded:

pytest-benchmark/src/pytest_benchmark/histogram.py

Lines 100 to 106 in c0d0104

	def make_histogram(output_prefix, name, benchmarks, unit, adjustment):
	if name:
	path = "{0}-{1}.svg".format(output_prefix, slugify(name))
	title = "Speed in {0} of {1}".format(TIME_UNITS[unit], name)
	else:
	path = "{0}.svg".format(output_prefix)
	title = "Speed in {0}".format(TIME_UNITS[unit])

Would it be possible to allow some customization of the prefix? I would like to change it to something like "Runtime in {0}".