Partial rewrite of includePattern function

This gives includePattern a repeatable import order, which is lexicographic by filename as defined in R5RS.

ie.
```
\includePattern "movements" ".*\\.ily$"
```
with folder
```
movements
├── 01.ily
├── 02.ily
├── 03.ily
└── 04.ily
```

it will generate
```
\include "movements/01.ily"
\include "movements/02.ily"
...
```

This is not the current behaviour.