TTR version 0.21-0
  Changes from version 0.20-2

NEW FEATURES:

- Added variable moving average function, VMA.

- Added Brian Peterson's price bands function, PBands.

- Added David Varadi's DVI indicator, DVI.


CHANGES:

- Added wilder and ratio arguments to DEMA. Thanks to Matthew Fornari for the
  suggestion.

- Changed wilderSum to seed initial value with raw sum. This matches Wilder's
  original calculations. Thanks to Mahesh Bp for the report.

- The BBands sd calculation now uses the population instead of sample
  statistic. This is consistent with Bollinger Band literature. Thanks to
  Jeff Ryan for the patch.


BUG FIXES:

- Fixed stockSymbols for nasdaq.com changes.

- Fixed ZLEMA default ratio by changing it from 2/(n-1) to 2/(n+1). This
  makes it consistent with EMA. Thanks to Dirk Eddelbuettel.

- Corrected close-to-close volatility. Thanks to James Toll for the report.

- adjRatios failed (spectacularly) if there were missing close prices. Thanks
  to Garrett See for the report.

