taxlist version 0.3.0

Improved code

Merge pull request #15 from ropensci/no-taxa

Solving issue with taxa v. 0.4.0

Changes in some links at documentation:

\doi instead of \url for articles

version 2.0 for CRAN

Updated version

Deprecated functions properly documented

Test for `summary()`

hierarchy misplaced in taxlist prototype

new function 'count_taxa'