First working version

Much has been deleted and much has changed.  The interface and
documentation will need to be refined and some of the deleted
functionality re-introduced.
Percent modern carbon

Changed terminology in help files to "percent modern carbon" and added
ordering checks for the calibration data.
General tidy
Small fixes
Quantile

Added functions to compute quantiles of coda objects
Fixed import of quantile
small fixes
Estimate sigma

The old metropolisDate is now metropolisDate0 and the new function
estimates sigma
small fixes.
Missing fix + predict rename

Fixed sigma estimation to allow for missing values.
Renamed carbonContent to fittedCarbon.
XL reads

Added slightly altered form of function to read from XL
superficial documentation updates
only enforce column type conversion if character
roxygenized
Merge pull request #1 from antarcticben/MorallyBankrupt

Morally bankrupt