Improve grammar and punctuation

Fix misspelling, improve grammar and punctuation.
I just looked up which were the rules for diphthongs and hiatus and this just added two more complexities to my life. I knew that words like `Abstraído` should have an orthographic accent, but I didn't know that `fluida` does not. Thanks for the correction!

In case anyone is curious (this is what I learnt today).

> 1. a, e, o are strong vowels, i, u are weak vowels. y is like i.
> 2. There can be only one strong vowel in a syllable, they never combine into a diphthong. ca-os, le-ón, le-er
> 3. When a strong and a weak vowel are next to each other (or separated by h) they form a diphthong. Eu-ro-pa, hia-to, rei-na
> 4. There are cases when a strong vowel is next to two weak vowels. In that case, they also form a diphthong. Pa-ra-guay, U-ru-guay
> 5. Finally, iu and ui are also diphthongs. The i is considered the strong vowel of the pair. Luis, viuda, Suiza
> 6. But when a weak vowel is in its own syllable, and the stress of the word falls on it, it gets an acute accent and the diphthong is broken. ca-í-do, sa-ú-co, rí-e

([Source](http://spanish.stackexchange.com/a/1535/90))