Add reader class

[NikolaJelic]

Added reader class that can can handle both file and string inputs.

class reader {
  std::vector<std::string> file_lines;
  std::unordered_map<std::string, std::string> key_value_pairs;
public:
  std::unordered_map<std::string, std::string> get_pairs();
  bool read_file(std::filesystem::path const &filename);
  bool read_file(std::string const &raw_string);
}

This class is currently working and able to extract, save and pass the stored unordered_map to other variables and objects.
Due to read_file() being and overloaded function and path and string being very similar when passed as literals, they first need to be initialized as variables of their respective type and passed to the function.
When passing the data as a string to the function, the key-value pairs need to be divided with the char /, as shown in the code below:

  pn::reader r;
  std::string raw_input = {"a=5/b=10/23=c"};
  std::filesystem::path filename{"test/test.ini"};
  r.read_file(filename); // r.read_file(raw_input);

For future implementation there is one more problem I noticed, that needs to be solved : the read_file() function doesn't take care of excessive white space at the start or end of the string which could cause problems during search.

[karnkaul]

I'd suggest not having a special character like / for text vs file input: both should converge on exactly the same code paths. You could simply use \n to simulate new lines in code.

[hentai-chan]

this line can be simplified, especially if you plan to add more files in the future it is not feasible to keep this list of files growing

[hentai-chan]

Sort your includes:

#include <iostream>   # std first
#include "pini.hpp"   # then your headers
#include "utils.hpp"

This is my personal preference, but there are also other otions.

[hentai-chan]

Weird lines breaks, I suggest you add a clang-format file to clean up your formatting everywhere.

[hentai-chan]

confusing line break, see also this mail from Linus as to why you don't have to adhere to the 80-column philosophy - in this case specifically, your code is harder to read because you make these unexpected line breaks