This will ignore files named `core` and `core.*` (except `core.c`,
`core.h`, `core.md`, `core.txt`) placed directly in the application
folder. This is where `make` is typically called and core dump due to
a crashing native application, flashing tool, or GDB would be placed.
The pattern is intentionally quite narrow, as there is e.g. a core
source folder that should still be monitored.
