Add news for v0.2.0 release

DESCRIPTION

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 Package: metacal
 Title: Bias estimation and calibration for metagenomics experiments
-Version: 0.1.0.9013
+Version: 0.2.0
 Authors@R: 
     person(given = "Michael",
            family = "McLaren",

NEWS.md

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+# metacal 0.2.0
+
+## New features
+
+### New estimation and calibration functions
+
+`estimate_bias()` and `calibrate()` provide easy-to-use high-level interfaces to the original metacal bias-estimation and calibration method.
+Their use is illustrated in the new tutorial.
+
+### New utility functions
+
+* `pairwise_ratios()` allows computing ratios between pairs of taxa and/or samples.
+
+* `perturb()` applies a compositional perturbation to all observations in an abundance matrix (or phyloseq object).
+
+### Support for phyloseq objects
+
+The new functions `estimate_bias()`, `perturb()`, `calibrate()`, and `pairwise_ratios()` all work with objects from the [phyloseq](https://joey711.github.io/phyloseq/) package as well as plain matrices. 
+Phyloseq is now a required dependency, though may be made optional in the future.
+
+### New tutorial
+
+The [new tutorial](https://mikemc.github.io/metacal/articles/tutorial.html) demonstrates the new estimation and calibration functions on a new dataset from [Leopold and Busby (2020)](https://doi.org/10.1016/j.cub.2020.06.011).
+
+## Minor fixes
+
+* Fixed failure of `coocurrence_matrix()` when names were missing (#5).
+
+# metacal 0.1.0
+
+Direct implementation of the methods described in [McLaren MR, Willis AD, Callahan BJ (2019)](https://elifesciences.org/articles/46923) and used for [the analysis of that paper](https://github.com/mikemc/mgs-bias-manuscript).