Rename rank(A::GrpAbFinGen) to torsion_free_rank

Unfortunately the notion of 'rank' for groups clashes with that for abelian groups.
The latter is also known as 'torsion free rank'. Hence I propose to rename `rank`
for abelian groups here accordingly.

docs/src/abelian/introduction.md

@@ -58,7 +58,7 @@ nrels(G::GrpAbFinGen)
 rels(A::GrpAbFinGen)
 isfinite(A::GrpAbFinGen)
 is_infinite(A::GrpAbFinGen)
-rank(A::GrpAbFinGen)
+torsion_free_rank(A::GrpAbFinGen)
 order(A::GrpAbFinGen)
 exponent(A::GrpAbFinGen)
 istrivial(A::GrpAbFinGen)

src/GrpAb/GrpAbFinGen.jl

@@ -35,7 +35,7 @@
 import AbstractAlgebra.GroupsCore: istrivial
 
 export abelian_group, free_abelian_group, is_snf, ngens, nrels, rels, snf, isfinite,
-       is_infinite, rank, order, exponent, istrivial, is_isomorphic,
+       is_infinite, torsion_free_rank, rank, order, exponent, istrivial, is_isomorphic,
        direct_product, is_torsion, torsion_subgroup, sub, quo, is_cyclic,
        psylow_subgroup, is_subgroup, abelian_groups, flat, tensor_product,
        dual, chain_complex, is_exact, free_resolution, obj, map,
@@ -476,12 +476,12 @@ is_finite_gen(A::GrpAbFinGen) = isfinite(snf(A)[1])
 ################################################################################
 
 @doc raw"""
-    rank(A::GrpAbFinGen) -> Int
+    torsion_free_rank(A::GrpAbFinGen) -> Int
 
-Return the rank of $A$, that is, the dimension of the
+Return the torsion free rank of $A$, that is, the dimension of the
 $\mathbf{Q}$-vectorspace $A \otimes_{\mathbf Z} \mathbf Q$.
 """
-rank(A::GrpAbFinGen) = is_snf(A) ? rank_snf(A) : rank_gen(A)
+torsion_free_rank(A::GrpAbFinGen) = is_snf(A) ? rank_snf(A) : rank_gen(A)
 
 rank_snf(A::GrpAbFinGen) = length(findall(x -> iszero(x), A.snf))