JSON output of e-index, R-index, and A-index should be floats and not strings

[cicirello]

Summary

When configured to generate a JSON output file, either in addition to SVG or instead of, the bibliometrics that are floating-point values (e-index, A-index, and R-index, and sometimes h-median) are output as strings in the JSON file rather than as floats. This is due to the formatting for the SVG to round to 2 decimal places. In the JSON output, it would be more desirable to output as floats with the available precision.