Add support for both 32-bit and 64-bit externals

The `architecture` key is now supported for externals.

Example:

```
externals:
  windows:
    - filename: blur-x86.dll
      name: blur
      architecture: 32
    - filename: blur-x64.dll
      name: blur
      architecture: 64
```

Version #0.9.3.0

Bump version # 0.9.21

Add levureStandaloneName()

Add note

Bump version # 0.9.13

Bump version # 0.9.12

Bump version #

Fix incorrect parameter type which triggers crash on macOS 10.14