Added support for float input in scientific notation and removed float rounding.

[sreeramsanjay]

Motivation

There is no support for floating-point inputs with scientific notation in the current implementation of miniWDL. Float values are rounded to 6 decimal points only; for example, floats smaller than 0.000001 are rounded to 0.0. Adding support for float input in scientific notation and removing float rounding using repr method to keep the input float value as is.
NOTE: floats smaller than 0.0001 will be return in scientific notations.

Approach

...

Checklist

• Add appropriate test(s) to the automatic suite
• Use make pretty to reformat the code with black
• Use make check to statically check the code using Pyre and Pylint
• Send PR from a dedicated branch without unrelated edits
• Ensure compatibility with this project's MIT license

[mlin]

@sreeramsanjay Sorry for the very slow uptake on this!

1. The serialization of a float to a string with six decimal places is required by the WDL spec (at least in a command placeholder). Are there other contexts where the serialization could be done differently consistent with the spec?
2. Can you supply a test case where reading a float with an exponent isn't working? I think it should generally, but specific bugs/oversights are possible certainly.