Float params accept JS string containing numeric characters

[jmarcosfer]

For reference when designing the tests in #66, and related to types like #27.

During manual testing of FrequencyBands I've found the following behaviour regarding its parameter types:

• Passing it a JS String for its frequencyBands parameter (which expects a VectorFloat in C++) does NOT produce an error, as would be expected. This is after converting the given frequencyBands array to a VectorFloat through the existing utility function arrayToVector, which means the function can successfully copy a JS String into a C++ VectorFloat. The result of the conversion for a 5-letter String is a vector of 5 NaNs. Essentia then does not complain about this VectorFloat of NaNs.
• Passing it a JS String for its float-typed sampleRate parameter produces an error only if the String contains text characters. However, it does not fail with a String containing numeric characters (such as "16000", instead of the JS Number of 16000). This means there is probably some sort of string->number type casting attempted somewhere in Embind, but I couldn't find any verification (checked here, here, here, here, and here).

I've opened a discussion on Emscripten's GitHub repository.