new_file_definition_: Helper function for 'new_file_definition()'
In a-maldet/readall: Read FWF, DSV, EXCEL And SAS Files

Helper function for new_file_definition()

new_file_definition_(
  file_path,
  file_structure,
  to_lower,
  cols_keep,
  extra_col_name = NULL,
  extra_col_val = NULL,
  extra_col_file_path,
  extra_adapters = new_adapters(),
  err_h = composerr("Error while calling 'new_file_definition_()'")
)

`file_path`	A string holding the path to the data file.
`file_structure`	A file_structure class object. This type of objects can be created by the functions `new_file_structure_fwf()`, `new_file_structure_dsv()`, `new_file_structure_excel()` or `new_file_structure_sas()` and fully defines the file structure of the data files. The idea is that a single file_structure can be valid for multiple data files and therefore be reused. Whereas a `file_definition` class object also holds the path to the file and is therefore only valid for a single file.
`to_lower`	A logical flag, defining if the names of the columns should be transformed to lower case after reading the data set (by calling `read_data()`). This transformation will be applied before comparing the column names (in the case of SAS-Files or DSV- and EXCE-Files with `header = TRUE`). In the case of `new_file_definition()` the `to_lower` argument overwrites the `to_lower` argument in the file_structure class object given in `file_structure`. If `to_lower` is omitted, then the `file_structure` class object remains unchanged. In the case of `new_file_definition_fwf()`, `new_file_definition_dsv()`, `new_file_definition_excel()` or `new_file_definition_sas()` the argument `to_lower` must either be `TRUE` or `FALSE`.
`cols_keep`	Either `TRUE` or a character vector. If set to `TRUE`, then all columns of the data are kept when calling `read_data()`. If `cols_keep` character vector, then the values in `cols_keep` represent the names of the columns, which are kept when calling `read_data()`.
`extra_col_name`	An optional string, which defines the column, which will be added to the data set (after reading it with function `read_data()`). Each entry of the column will have the single value given in `extra_col_val`. For example: This column is useful when reading similar data files for separate years (one could pass the current data set year to `extra_col_name` and set `extra_col_name = "year"`). If `extra_col_name` is omitted, no column will be added to the data set and then `extra_col_val` must be omitted as well. additional column with the column name, given in `extra_col_name`. If omitted, then no column will be added to the data set and the argument `extra_col_name` must be omitted as well.
`extra_col_val`	An optional value (any atomic type), which will be added (after reading the data set with function `read_data()`) as an additional column with the column name, given in `extra_col_name`. For example: This column is useful when reading similar data files for separate years (one could pass the current data set year to `extra_col_name` and set `extra_col_name = "year"`). If omitted, then no column will be added to the data set and the argument `extra_col_name` must be omitted as well.
`extra_col_file_path`	Either `FALSE` or a string. If set to `FALSE` no file-path-column will be added to the data set, when calling `read_data()`. If the argument `extra_col_file_path` is a string, then a column holding the file path of the data file will be added to the read data set, when calling `read_data()`. The string of `extra_col_file_path` will be used as column name for this additional column.
`extra_adapters`	An optional adapters class object, which holds a list of adapter functions. These adapter functions will be added to the adapter functions already stored in the file_structure class object. For further details on adapter functions see section adapters.
`err_h`	An error handler