CLI does not support arguments specified in scientific notation #10
Description
One cannot specify target rms error in scientific notation, e.g., as -r 1e-6. Rather, this must be specified as -r 0.000001. This becomes cumbersome when integrating tthresh with other tools (like awk) that output very small or large floating-point numbers in scientific notation.
Can the is_number() function be replaced with something based off sscanf(), which parses numbers in any format supported by printf()? For example, one could specify a number like 2-23 (single-precision machine epsilon) as 0x1p-23.