Added new methods/functions

methods:
 - sort
 - trim
 - seqinfo
 - gi-gi findOverlaps

added countsBetweenAnchors to import

added .isSortedChrom, .isSortedStart, .isEqualSeqInfo to library (not
exported)

added dependencies on GenomeInfoDb and BioGenerics (were implicit
previously)

built documnetation