Include circular diagrams in label tests (currently limited support)
Explicitly test default vs 'start' for feature labels.

This awaits a code change to see if the desired change worked.
Support feature label_position of middle/center/centre on circular diagrams

These values are already supported on the linear GenomeDiagrams,
so it makes sense to offer them on circular GenomeDiagrams too.
Thanks for David Martin for alternative implementation and sharing
a motivating usecase, and his pull request:
https://github.com/biopython/biopython/pull/116

This commit included an attempt to refactor the label placement
code to reduce code duplication and simplify further work here.
(cherry picked from commit a50a440f1e49ca08829194e11339c978db7286a3)
Support feature label_position of start/end on circular diagrams
Explicitly use default label placement in this test
Mention circular GenomeDiagram figures now support label_position in NEWS, thank David Martin
Move circular GenomeDiagram feature labels outside sigil

This now matches the linear GenomeDiagrams, but is a break in
backwards compatibility, and may require us to review the default
spacing between tracks.
GenomeDiagram feature label_strand property
Mention moving circular GenomeDiagram labels in NEWS
Layout tweak for circular GenomeDiagram feature labels
Mention mmCIF changes in NEWS and DEPRECATED files

Documentation change only, no need for TravisCI [ci skip]
TravisCI doesn't have a fasttree package

$ sudo apt-get install clustalw clustalo fasttree | tail -n 2
E: Package 'fasttree' has no installation candidate
is only available from another source

(This wasn't breaking the builds, but did mean clustal wasn't
being installed and so those tests were skipped.)
Generalise internal function in chromosome diagram code
Refactoring chromosome diagram label code
Support optional fill color on chromosome diagrams
Test optional fill color on chromosome diagrams
Use feature fill colour as label background on chromsome diagrams

Based on an earlier hack from Oct 2011, which like the recently
committed fill color, was used in figures in Jupe et al. (2012)
http://dx.doi.org/10.1186/1471-2164-13-75
Test strand specific chromosome diagrams labels with background color
SeqIO: Give better error message on invalid sequence length string

Signed-off-by: Kai Blin <kai.blin@biotech.uni-tuebingen.de>
Handle named feature colors as strings in chromosome diagrams