Vendor dependencies for 0.3.0 release

vendor/const_soft_float/README.md

@@ -0,0 +1,58 @@
+# Rust float-point in constant context
+
+Floating-point code is from `compiler_builtins = "0.1.94"` and `libm = "0.2.6"`, and has been rewritten for use in a constant context. 
+
+Fuzzing of all operations is performed against the relevant reference code to ensure correctness of the port, but please open an issue if there is any inconsistent behavior.
+
+Exported Soft Float Types:
+* `SoftF32` 
+* `SoftF64`
+
+Features:
+* `no_std` - Enabled by default
+* `const_trait_impl` - For const operator implementations
+* `const_mut_refs` - For const operator with assignment implementations
+
+On `stable`:
+```
+const fn const_f32_add(a: f32, b: f32) -> f32 {
+    SoftF32(a).add(SoftF32(b)).to_f32()
+}
+```
+
+On `nightly` with `const_trait_impl` usage:
+```
+const fn const_f32_add(a: f32, b: f32) -> f32 {
+    (SoftF32(a) + SoftF32(b)).to_f32()
+}
+```
+
+On `nightly` with `const_mut_refs` usage:
+```
+const fn const_f32_add(a: f32, b: f32) -> f32 {
+    let mut x = SoftF32(a);
+    x += SoftF32(b);
+    x.to_f32()
+}
+```
+<br>
+
+Implemented `const` Functions:
+- `from_(f32/f64)`
+- `to_(f32/f64)`
+- `from_bits`
+- `to_bits`
+- `add`
+- `sub`
+- `mul`
+- `div`
+- `cmp`
+- `neg`
+- `sqrt`
+- `powi`
+- `copysign`
+- `trunc`
+- `round`
+- `floor`
+- `sin`
+- `cos`