Add function to create histograms with variable bin widths.

[markdalton]

Almost an exact duplicate of the existing function but with variable bin widths.

[gluex]

Test status for this pull request: SUCCESS

Summary: /work/halld/pull_request_test/sim-recon^dalton_histogram_fill/tests/summary.txt Logs: /work/halld/pull_request_test/sim-recon^dalton_histogram_fill/tests/log

Build log: /work/halld/pull_request_test/sim-recon^dalton_histogram_fill/make_dalton_histogram_fill.log Build report: /work/halld/pull_request_test/sim-recon^dalton_histogram_fill/report_dalton_histogram_fill.txt Location of build: /work/halld/pull_request_test/sim-recon^dalton_histogram_fill