Added detach methods

Detach methods prune a node from a tree and return it as a new
Phylogeny variable with the root set as the detached node.
Added midpoint finding method and rewritten distance and depth methods
Removed the "get" and "set" from functions as per #25
Updated Method for reading in PhyloXML files
Corrected syntax error in PhyNode constructor
Updated constructor for Phynode
Corrected error.
Typo correction
Merge branch 'Ward9250PhyloV1' of github.com:Ward9250/Bio.jl into phylodocs

Conflicts:
	src/phylo/typedefs.jl