Data format for a read-only LDAP data store.  LDAP defines access to
records, each of them having n attributes.  Mandatory attributes are
"dn" and "objectClass".

The string table stores all strings, zero-terminated.

An Index is an array of uint32_t, each an offset inside the file to the
corresponding string.

Each Record is an array of uint32_t, each an offset inside the file to
the corresponding string.  Entries are in pairs, where the first
uint32_t points to the attribute name, the second points to the
attribute value.  Each record starts with a pair <number-of-attributes,0>.
The number of attributes equals the number of 64-bit pairs (including
this length pair itself).  The second pair is
<value-of-dn,value-of-objectClass>, the following pairs are all
<name-of-attribute,value-of-attribute>.

The Record Index is a table of offsets to the corresponding record.

All integers are stored LITTLE ENDIAN.

  const uint32_t magic = 0xfefe1da9;  /* 1da9 == "LDAP" ;-) */
  uint32_t attribute_count, record_count, indices_offset, size_of_string_table;
  char string_table[size_of_string_table];
  uint32_t attribute_names[attribute_count];
  uint32_t attribute_flags[attribute_count];  /* 1: match case insensitively */
  uint32_t records[record_count][];  /* in the same order as the records
                                        are physically on disk */
/* indices_offset points here */
  uint32_t record_index[record_count];
  struct {
    uint32_t index_type;  /* 0 == sorted array of pointers, rest reserved */
    uint32_t next;        /* offset of next index */
    /* for index_type==0: */
    uint32_t indexed_attribute; /* offset of attribute name */
    uint32_t record_offsets[record_count];
  }

The indices are at the end to make it possible to add more indices.
The next pointer is there to make extensions possible.