removed dependency on plm and formula.tools
add function blockBootSample for block bootstrapping with panel data
add option in makeDist to force the values of the distribution function be between 0 and 1
Update rhs.vars to fix bug related to formulas like y~x+I(x^2)
Update toformula to allow for no right hand side variables
Added function to take distribution functions (ecdf objects) and turn them into step functions for the quantiles.
Improved code for working with formulas