You are given a string sentence that consist of words separated by spaces. Each word consists of lowercase and uppercase letters only. We would like to convert the sentence to "Goat Latin " (a made-up language similar to Pig Latin.) The rules of Goat Latin are as follows: If a word begins with a vowel ('a', 'e', 'i', 'o', or 'u'), append "ma " to the end of the word. For example, the word "apple " becomes "applema ". If a word begins with a consonant (i.e., not a vowel), remove the first letter and append it to the end, then add "ma ". For example, the word "goat " becomes "oatgma ". Add one letter 'a' to the end of each word per its word index in the sentence, starting with 1.