Conversion from CamelCase
Your mission is to convert the name of a function from CamelCase ("MyFunctionName") into the Python format ("my_function_name") where all chars are in lowercase and all words are concatenated with an intervening underscore symbol "_".
Input: A function name as a CamelCase string (string).
Output: The same string (string), but in under_score.
Examples:
assert.strictEqual(fromCamelCase("MyFunctionName"), "my_function_name");
assert.strictEqual(fromCamelCase("IPhone"), "i_phone");
How it is used: To apply function names in the style in which they are adopted in a specific language (Python, JavaScript, etc.).
Precondition:
0 < len(string) <= 100
Input data won't contain any numbers.
