changed Formula to FormulaTerm in documentation and docstrings (#322)

Fixes #321.

Author: ajinkya-k

docs/src/contrasts.md

@@ -63,7 +63,7 @@ ContrastsCoding
 
 ## Further details
 
-### Categorical variables in `Formula`s
+### Categorical variables in `FormulaTerm`s
 
 Generating model matrices from multiple variables, some of which are
 categorical, requires special care.  The reason for this is that rank-$k-1$
@@ -93,7 +93,7 @@ categorical `a`, `b`, and `c`:
     * The `a` in `a&b` is *non-redundant* because it aliases `b`, which is not
       present anywhere else in the formula.
 
-When constructing a `ModelFrame` from a `Formula`, each term is checked for
+When constructing a `ModelFrame` from a `FormulaTerm`, each term is checked for
 non-redundant categorical variables.  Any such non-redundant variables are
 "promoted" to full rank in that term by using [`FullDummyCoding`](@ref) instead
 of the contrasts used elsewhere for that variable.

src/contrasts.jl

@@ -263,7 +263,7 @@ Not exported but included here for the sake of completeness.
 Needed internally for some situations where a categorical variable with ``k``
 levels needs to be converted into ``k`` model matrix columns instead of the
 standard ``k-1``.  This occurs when there are missing lower-order terms, as in
-discussed below in [Categorical variables in Formulas](@ref).
+discussed below in [Categorical variables in FormulaTerms](@ref).
 
 # Examples
 

src/formula.jl

@@ -23,7 +23,7 @@ catch_dollar(ex::Expr) =
 """
     @formula(ex)
 
-Capture and parse a formula expression as a `Formula` struct.
+Capture and parse a formula expression as a `FormulaTerm` struct.
 
 A formula is an abstract specification of a dependence between _left-hand_ and
 _right-hand_ side variables as in, e.g., a regression model.  Each side
@@ -32,7 +32,7 @@ matrix suitable for modeling.  This specification looks something like Julia
 code, is represented as a Julia `Expr`, but uses special syntax.  The `@formula`
 macro takes an expression like `y ~ 1 + a*b`, transforms it according to the
 formula syntax rules into a lowered form (like `y ~ 1 + a + b + a&b`), and
-constructs a `Formula` struct which captures the original expression, the
+constructs a `FormulaTerm` struct which captures the original expression, the
 lowered expression, and the left- and right-hand-side.
 
 Operators that have special interpretations in this syntax are