swap getMappedReadOpt in for getMappedRead
sequencedSingleBase returns Option, doesn't throw
getMappedReadOpt change that got lost in merging
rename mdTag{,String} fields to reflect Optionness
move Read.scala into its own 'reads' package

- it has a lot of classes in it already, which I would like to break
out
- org.bdgenomics.guacamole package becoming a bit of a kitchen sink
- prefer code only in "leaf" packages
put {Un,}MappedReadSerializer in their own files
case-class-ify MateProperties

- put an optional instance in each of {Un,}MappedRead
  - it is Some() iff former isPaired boolean would have been true
- give it its own ser/deser classes, called by *MappedReads'
Merge remote-tracking branch 'origin/master' into option-ify

Conflicts:
	src/main/scala/org/bdgenomics/guacamole/reads/Read.scala
PR feedback
Merge remote-tracking branch 'origin/master' into option-ify

Conflicts:
	src/test/scala/org/bdgenomics/guacamole/DistributedUtilSuite.scala
	src/test/scala/org/bdgenomics/guacamole/ReadSuite.scala
	src/test/scala/org/bdgenomics/guacamole/TestUtil.scala
	src/test/scala/org/bdgenomics/guacamole/callers/SomaticLogOddsVariantCallerSuite.scala
add comment to CanSerializeMatePropertiesOption
Merge pull request #150 from hammerlab/option-ify

Make a couple of `Read` getters return `Option`s rather than throwing