v0.4.0

- `--mt4-terminal DIR` and `--mt5-terminal DIR` compile with the MetaEditor and standard library of a portable terminal you already have, instead of the cached install. The folder is mounted read-only and nothing is written into it, except the `.ex4`/`.ex5` of a source compiled from inside its own `MQL4`/`MQL5` folder. The cached toolchain stays as it was. A folder without MetaEditor, or whose terminal has never been started and so has not unpacked its standard library, is exit `2`. `--version` with the option reports that terminal's build.
- A platform given its own terminal is never downloaded or installed, and a compile now installs only the platforms its sources need. Before, the first run always installed both MT4 and MT5; now a first run of only `.mq5` files installs MT5 alone, and MT4 follows the first time a `.mq4` is compiled. `--setup`, `--update` and `--watch` still install both.