0.15.0

Merge Wasmtime dotnet into repo.

* 'master' of wasmtime: (28 commits)
  Fix typo in Memory.Maximum doc string. (#1432)
  Add Wasmtime C API function to control linker shadowing.
  Fix typo in exception message.
  Fix typo in method call.
  Reimplement the C# API.
  Support WASI snapshot0 in the C API.
  Add a .gitattributes file to specify eol=LF (#1370)
  Add a wasmtime-specific `wasmtime_wat2wasm` C API (#1206)
  Be explicit when marshalling bool.
  Change `wasm_module_new` to use `Module::from_binary`.
  Bump .NET NuGet package version to 0.12.0
  Rename `wasi_config_set_std[in|out|err]`.
  Favor using non-braced using statement.
  Loop the array of strings only once.
  Ensure marshaled UTF-8 string arrays are null terminated.
  Fix unit tests on Windows.
  Add WASI unit tests for the C# API.
  Implement WASI C API.
  Move the C API to a separate crate (#818)
  Add tests calling function imports.
  ...