Ovf

API changes for improved generality.
- added `ovf_file_initialize` and `ovf_segment_create` to API. This enables either defaulting the values of an object or creating a new one (which includes the initialization), enabling better C++ wrapping
- changed integer definitions of OVF formats
- also some minor aesthetic changes

Bugfixes
- Fixed reading binary data containing line breaks
- fixed "appending" to a nonexistent file, which should now correctly create the file
- Due to the nature of binary data, it may randomly contain line breaks. It is now parsed until the "End: Data" statement is encountered
- other minor things

The C struct contained `int`s instead of `bool`s, which is now fixed. This removes a bug in the Python bindings, which would not correctly show if a file's `is_ovf` was `true`.

- significantly improved adherence to the OVF 2.0 specifications
- improved the description of the specifications in the Readme
- using the PEGTL for parsing to improve predictability, stability , performance, etc.

- binary is now ensured to be written as little endian IEEE standard floating point
- binary is always read with the assumption of little endian IEEE standard floating point
- corrected some misinterpreted keywords
- added better error messages for missing keywords
- irregular meshtype is now functioning
- capitalisation is now ignored correctly

- some bugfixes in the Fortran bindings
- empty lines, comment lines and empty lines containing a comment are now correctly ignored

- Segments can now be initialised by function call in Fortran and C
- Segments are now automatically initialised on construction in Python
- Fixed some possible segmentation faults in bindings
- Also made Filter_File_Handle header only
- Also updated fmtlib

- fixed a bunch of small bugs
- improved library structure
- minor changes to `ovf_segment` and `ovf_file`
- added Fortran bindings, included in CMake by default

A lot of cases may still crash, but a few basic tests are already running.

*This is the initial design of the API, which may therefore change a lot in coming releases!*