Replace roff man pages with asciidoctor

This replaces the generation of man pages on project setup
by a on-demand generation via asciidoctor.
An exception are the man pages for the commands `day`, `month`, and `week`
which are simply redirects to the man page `timew-chart.1`. Those are now
static files in the Timewarrior repository.

A CMake find module to detect asciidoctor was added.
If asciidoctor is found, the targets `doc`, `man1`, and `man7` are created.
Those targets are also added to the default build target.

If asciidoctor is not available, the target `doc` is available, but it only
emits a message to install asciidoctor first.

Signed-off-by: Thomas Lauf <thomas.lauf@tngtech.com>

doc/man7/CMakeLists.txt

@@ -0,0 +1,21 @@
+cmake_minimum_required (VERSION 2.8.12)
+
+file (GLOB DOC_SOURCES "${CMAKE_CURRENT_BINARY_DIR}/*.7.adoc")
+set (DOC_FILES)
+
+foreach (SRC ${DOC_SOURCES})
+  string (REPLACE ".adoc" "" OUTPUT_FILE_NAME "${SRC}")
+
+  add_custom_command (
+          OUTPUT "${OUTPUT_FILE_NAME}"
+          COMMAND ${ASCIIDOCTOR_EXECUTABLE} -b manpage ${ASCIIDOCTOR_OPTIONS} ${SRC} -o ${OUTPUT_FILE_NAME}
+          DEPENDS "${SRC}")
+
+  set (DOC_FILES ${DOC_FILES} "${OUTPUT_FILE_NAME}")
+endforeach (SRC)
+
+add_custom_target (man7 DEPENDS ${DOC_FILES})
+
+install (DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+         DESTINATION ${TIMEW_MANDIR}
+         FILES_MATCHING PATTERN "*.7")