math: remove logb

As discussed in #12112, this is a false friend (the libc logb()
does something else), and without keyword arguments or at least
function overloading, this is hard to read.
Better use "/ log(base)" trick.

CHANGELOG.rst

@@ -7,10 +7,6 @@ Notable improvements and fixes
 Deprecations and removed features
 ---------------------------------
 
-Scripting improvements
-----------------------
-- ``math`` gained a new ``logb`` function.
-
 Interactive improvements
 ------------------------
 - When typing immediately after starting fish, the first prompt is now rendered correctly.

doc_src/cmds/math.rst

@@ -153,11 +153,9 @@ Functions
 ``ln``
     the base-e logarithm
 ``log`` or ``log10``
-    the base-10 logarithm
+    the base-10 logarithm. To compute the logarithm for an arbitrary base ``b``, use ``log(x) / log(b)``.
 ``log2``
     the base-2 logarithm
-``logb(b,x)``
-    returns the logarithm with base b of x
 ``max``
     returns the largest of the given numbers - this takes an arbitrary number of arguments (but at least one)
 ``min``

src/tinyexpr.rs

@@ -291,7 +291,6 @@ fn npr(n: f64, r: f64) -> f64 {
     (L!("log"), Function::Fn1(f64::log10)),
     (L!("log10"), Function::Fn1(f64::log10)),
     (L!("log2"), Function::Fn1(f64::log2)),
-    (L!("logb"), Function::Fn2(|base, x| x.log(base))),
     (L!("max"), Function::FnN(maximum)),
     (L!("min"), Function::FnN(minimum)),
     (L!("ncr"), Function::Fn2(ncr)),

tests/checks/math.fish

@@ -276,20 +276,10 @@ echo $status
 math 'log2(8)'
 # CHECK: 3
 
-math 'logb(2, 8)'
-# CHECK: 3
-math 'logb(67, 406067677556641)'
-# CHECK: 8
-math 'logb(42, 230539333248)'
-# CHECK: 7
-math 'logb(12, 8916100448256)'
-# CHECK: 12
-math 'logb(3, 5559060566555523)'
-# CHECK: 33
-math 'logb(5, 2384185791015625)'
-# CHECK: 22
-math 'logb(7, 343)'
+math 'log(8) / log(2)'
 # CHECK: 3
+math 'log(625) / log(5)'
+# CHECK: 4
 
 # same as sin(cos(2 x pi))
 math sin cos 2 x pi