Function open

open(path, flags, mode?): Promise<FileHandle>
Opens the file at the given path. Opening flags:
- r: open for reading
- w: open for writing, truncating the file if it exists
- x: open with exclusive creation, will fail if the file exists
- a: open for writing, appending at the end if the file exists
- +: open for updating (reading and writing)
```
const f = await tjs.open('file.txt', 'r');
```
Parameters
- path: string
  The path to the file to be opened.
- flags: string
  Flags with which to open the file.
- Optionalmode: number
  File mode bits applied if the file is created. Defaults to 0o666.
Returns Promise<FileHandle>