Support for intializing SuchTree with a Newick string

[ryneches]

It would be cool to be able to initialize new SuchTree objects like this :

T1 = SuchTree( '~/data/mytree.tree' )
T2 = SuchTree( 'http://example.com/data/mytree.tree' )
T3 = SuchTree( '(A:0.1,B:0.2,(C:0.3,D:0.4):0.5);' )