Merge #36

36: Parse ELF lazily r=stlankes a=mkroening

Closes https://github.com/hermitcore/rusty-loader/issues/32.

This reduces allocations using an example kernel from

```console
[LOADER] Allocating 0x268 bytes at 0x11ACC0, index 0
[LOADER] Allocating 0x8B8 bytes at 0x11AF40, index 640
[LOADER] Allocating 0xD0 bytes at 0x11B840, index 2944
[LOADER] Allocating 0xE0 bytes at 0x11B940, index 3200
```

to

```console
[LOADER] Allocating 0x268 bytes at 0x117E00, index 0
[LOADER] Allocating 0xD0 bytes at 0x118080, index 640
```

Co-authored-by: Martin Kröning <mkroening@posteo.net>
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