Alv

* Added support for selecting sub-alignments. See option `-sa`

* Ed Davies fixed a bug: sorting using option -so was broken

* What??

* Added the option --alignment-index to support files with multiple MSAs.
* Added two functions, view and glimpse, to enable use of alv in notebook environments.

* Fixed accession abbreviation so that short accessions are left as they are.
* Requiring python 3.5 or later, because Colorama has droppen support for 3.4.

* New options: --only-variable and --only-variable-excluding-indels, contributed by nikostr. Constrains coloring
to columns with variation and variation not counting indels.
* Fixed the --dotted option, which only worked with the first block for DNA sequences. Also improved the coloring
which was too ugly in dotted mode (due to laziness).