GEOMESA-138 encode avrosimplefeature field name

included tests
I had asked @aannex-ccri to use the `match` here, in part to practice Scala, and in part to keep the internal names relatively brief (by not encoding characters that don't need it).  That having been said, I'm open to other choices for this.  If there's reason to believe that hex-encoding the string would be faster than the regex + recursion, I have no objections to it changing in that direction.