Add changes for release v15.0.0

This commit adds all the changes prototyped for the release `v15.0.0`. Those
changes are:

- Rename option `--modified-date` to `--modification-date`.
- Remove "SOURCE CODE" section from help and rewrite some parts of it.
- Transform some macros into functions.
- Use new enums, `Parse_Status` and `Return_Status`, instead of `int` to make
  function returns more legible.
- Standard library functions will now include the `std` namespace in all of
  their uses.
- Some error reports have been slightly changed.
- Add new compilation option `-std=c++11`.
- Add a `.clang-format` file to automatically format files.
- Revealing user and group will no longer use static pointers, but a buffer on
  the stack.

.clang-format

@@ -0,0 +1,2 @@
+BasedOnStyle: Microsoft
+ColumnLimit: 80

Makefile

@@ -1,7 +1,7 @@
 SOURCES_DIRECTORY = sources
 BINARIES_DIRECTORY = binaries
 COMPILER = g++
-COMPILER_OPTIONS = -Oz -Wall -Wextra -Werror
+COMPILER_OPTIONS = -std=c++11 -Oz -Wall -Wextra -Werror
 
 all: ${BINARIES_DIRECTORY}/reveal