Now handle missing data / add demos
- revised
plot.twoway()to use and default to na.rm=FALSE - revised
plot.twoway.fit()to use and default to na.rm=FALSE - revised
meanfit()to use and default to na.rm=FALSE - revised
twoway.default()to pass ... (hence na.rm) to meanfit - added demo/ directory
- added demo/example-na.r to illustrate use of na.rm
- added demo/00Index
- Turn on travis CI