New keys:

- bookmark prompt (^B)
- pin directory (B)

The intention of the change is to facilitate opening the bookmark prompt in
navigate-as-you-type mode. The bookmark prompt is used more than the pin
current directory option.

Enabled functionality:

- Copy file path (^K)
- Run desktop search utility (^/)
- Rename file (^R)
- Open with... (^O)
- Pin current directory (^B)
- Visit pinned directory (^V)
- Extract archive (^X)

- For standard view, use ISO 8601 date format.
- For detailed view (i.e. stat), use default Linux date
  format. Also, remove GMT offset to avoid confusion in
  determining source of offset when reading alongside
  the local time zone.

1. File name comparison method:
 - initially ignore white space and punctuation characters
 - run test for numeric values
 - if the remaining substrings match in case-insensitive compare, compare case
 - if they still match, see which one has more prefix symbols
 - if they still match, run a case-sensitive compare on complete strings

2. Fixed xstrcmp() to return diff instead of 0 and -1.

Results in even less memory usage. The names are appended one after another.
The offsets are reset when the location of the memory changes die to realloc().

Other changes:

1. Use a debug mode print to measure time.
2. Remove redundant prefix when printing pointers in debug mode.