Fix some mistakes in doxygen docs for ding-libs.

[alexey-tikhonov]

Cloned from https://pagure.io/SSSD/ding-libs/issue/2307 :

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Here are some review comments from Stephen but I suspect there is much more so it makes sense to have a run of it.

                          struct ini_cfgfile **file_ctx);

 /**
+ * @brief Create a configuration file object using memory buffer.

@brief Create a configuration file object from a NULL-terminated buffer.

+ *
+ * Create a file object for parsing a configuration file.
+ * Configuration will use provided memory instead of the actual file.

Configuration will use the provided memory buffer instead of a real file.

+ *
+ * A "configuration file object" is different from
+ * a "configuration object". The former stores metadata
+ * about a file the configuration data is read from,

about a file from which the configuration data is read,
(this is a very esoteric bit of English)

+ * while the latter holds the configuration itself.

while the latter holds the configuration data itself.