calc/README: Add mention of logarithmic units.
calc/calc-help.el (calc-logunits-add): Rename from `calc-logunits-plus'.
(calc-logunits-sub): Rename from `calc-logunits-minus'.
(calc-logunits-mul): Rename from `calc-logunits-times'.
(calcFunc-lupoweradd): Rename from `calcFunc-lupowerplus'.
(calcFunc-lupowersub): Rename from `calcFunc-lupowerminus'.
(calcFunc-lupowermul): Rename from `calcFunc-lupowertimes'.
calc/calc-ext.el (calc-init-extensions): Change names of logarithmic
unit functions in autoloads.