Converts a params map into multipart field tuples.
BoldSign's multipart API uses bracket notation for nested objects:
signers[0][name]="Neil"signers[0][formFields][0][bounds][x]="50"
Recursively flattens arbitrarily nested maps and lists. Use
form_multipart/1 for Req's :form_multipart option.
Summary
Functions
Splits files from params and returns {file_parts, field_parts}.
Flattens a map into form field tuples with recursive bracket notation.
Returns Req-compatible multipart parts.