When using a clean build dir the install failed as it referenced
a non-existing `regorus_ffiCorrosion.cmake` file. I believe I used
the shorter `regorus_ffi` as my `EXPORT` in the `corrosion_install`
at some point and then later didn't notice that I referenced a stale
generated file when I initially handed in this PR. We must make sure
that the same identifier is used here too. See also the documentation
from `corrosion_install`:
> * **EXPORT**: Creates an export that can be installed with `install(EXPORT)`. <export-name> must be globally unique.
> Also creates a file at ${CMAKE_BINARY_DIR}/corrosion/<export-name>Corrosion.cmake that must be included in the installed config file.
This leverages the still-undocumented `corrosion_install` to get
an installable ffi binding that can be consumed by other projects,
e.g. from yocto:
```
$ ninja install
[4/5] Install the project...
-- Install configuration: "Debug"
-- Up-to-date: /home/milian/projects/compiled/regorus-test/lib/libregorus_ffi.so
-- Up-to-date: /home/milian/projects/compiled/regorus-test/include/regorus_ffi/regorus.hpp
-- Up-to-date: /home/milian/projects/compiled/regorus-test/include/regorus_ffi/regorus.ffi.hpp
-- Up-to-date: /home/milian/projects/compiled/regorus-test/lib/cmake/regorus_ffi/regorus_ffi_targets.cmake
-- Up-to-date: /home/milian/projects/compiled/regorus-test/lib/cmake/regorus_ffi/regorus_ffiConfig.cmake
-- Up-to-date: /home/milian/projects/compiled/regorus-test/lib/cmake/regorus_ffi/regorus_ffiCorrosion.cmake
```
This can then be consumed as such:
```
find_package(regorus_ffi CONFIG REQUIRED)
add_executable(test test.cpp)
target_link_libraries(test PRIVATE regorus_ffi::regorus_ffi)
```
