support for annotating the ends of variants (for CNVs and SVs)

This release adds much more test-coverage (>80%).

It also provides a feature for annotating large variants where we want to know about, e.g. the breakpoints of structural variants. If the -ends flag is specified from the command-line, then in addition to the annotation of the entire interval (as in the default mode), each variant will be annotated by what overlaps its 1-base left end (prefixed by "left_") and its 1-base right end (prefixed by "right_"). The left and right annotations are only done for intervals longer than 1-base.

It also adds the -permissive-overlap flag which tells vcfanno that any overlap is sufficient to add an annotation. In default mode, it requires that they also share the REF and at least 1 ALT allele. (this is used implicitly for the above -ends parameters).