Allow compilation with FreeBSD/clang.

Update intersect.rst

update the output from "-u" option.

Update the format on code block

Add human hg38 genome file

Update overview.rst

Correction: redistrubute --> redistribute

Created with the UCSC fetchChromSizes [1] tool:

    fetchChromSizes hg38 > genomes/human.hg38.genome

[1] http://hgdownload.cse.ucsc.edu/admin/exe/linux.x86_64/fetchChromSizes

fix -slop with -pct

Fisher's Exact Test

Various warning fixes redux

Remove extra parentheses that clang thinks are there to prevent a
different warning for "if (numConsumedByB = 0) /*assignment intended*/".
Use 0 instead of NULL to initialise non-pointers.
Only const *integral or enumeration* static data members can be portably
initialised within the class definition.

...so that namespace "std" already exists when we try to use it,
as it will have been declared by the standard headers #included.
Doing otherwise elicits a warning from clang.

Update links in docs to point to the bedtools2 github pages.

Added new -iobuf option and unit tests.