calc.texi (Simplification modes): Mention "basic" simplification.

calc.texi (Simplification modes): Mention "basic" simplification.
(The Calc Mode Line): Mention the mode line display for Basic
simplification mode.
(Simplify Formulas): Refer to 'algebraic' rather than 'default'
simplifications.
(Basic Simplifications): Rename from "Limited Simplifications"
Replace "limited" by "basic" throughout.
(Algebraic Simplifications):  Indicate that the algebraic
simplifications are done by default.
(Unsafe Simplifications):  Mention `m E'.
(Simplification of Units): Mention `m U'.
(Trigonometric/Hyperbolic Functions, Reducing and Mapping,
Kinds of Declarations, Functions for Declarations):  Mention
"algebraic simplifications" instead of `a s'.