CRAN Release version 0.4.0

• Changed the name of lm_tip() to tip_lm()
• The API has been fundamentally updated so that the functions now take a numeric value as a first argument rather than a data frame.
• Added adjust_* functions to allow for specification of all unmeasured confounder qualities without tipping
• Split tip_* functions into hazard ratio, odds ratio, and relative risk
• Add R2 parameterization with tip_coef_with_r2(), adjust_coef_with_r2(), and r_value()