CHANGES IN OPTMATCH VERSION 0.7

NEW FEATURES
* New function fill.NAs replaces missing observations (ie. NA values) with minimally informative values (ie. the mean of observed columns). Fill.NAs handles functions in formulas intelligently and provides missing indicators for each variable. See the help documentation for more information and examples.

BUG FIXES
* mdist.function method now properly returns an optmatch.dlist object for use in summary.optmatch, etc.
* mdist.function maintains label on grouping factor.

CHANGES IN OPTMATCH VERSION 0.6-1
NEW FEATURES
* New mdist method to extract propensity scores from models fitted using bigglm in package "biglm".
* mdist's formula method now understands grouping factors indicated with a pipe ("|")
* informative error message for mdist called on numeric vectors
* updated mdist documentation

CHANGES IN OPTMATCH VERSION 0.6

NEW FEATURES
* There is a new generic function, mdist(), for creating matching distances.  It accepts: fitted glm's, which it uses to extract propensity distances; formulas, which it uses to construct squared Mahalanobis distances; and functions, with which a user can construct his or her own type of distance.  The function method is more intuitive to work with than the older makedist() function.  
* A new function, caliper(), builds on the mdist() structure to provide a convenient way to add calipers to a distance.  In contrast to earlier ways of adding calipers, caliper() has an optional argument specify observations to be excluded from the caliper requirement --- this permits one to relax it for just a few observations, for instance.
* summary.optmatch() now removes strata in which matching failed (b/c the matching problem was found to be infeasible) before summarizing.  It also indicates when such strata are present, and how many observations fall in them.
* Demo has been updated to reflect changes as of version 0.4, 0.5, 0.6.

DEPRECATED & DEFUNCT
* The vignette is sufficiently out of date that it's been removed.  

BUG FIXES
* subsetting of objects of class optmatch now preserves matched.distances attribute.
* fixed bug in maxControlsCap/minControlsCap whereby they behaved unreliably on subclasses within which some subjects had no permissible matches.  
* Removed unnecessary panic in fullmatch when it was given a min.controls argument with attributes other than names (as when it is created by tapply()).
* fixed bug wherein summary.optmatch fails to retrieve balance tests if given a propensity model that had function calls in its formula.
* Documentation pages for fullmatch, pairmatch filled out a bit.

Changes in optmatch version 0.5
New features:
* summary.optmatch() completely revised.  It now reports information about
the configuration of the matched sets and about matched distances.  In 
addition, if given a fitted propensity model as a second argument it 
summarizes covariate balance.
