Build and install docs by default

Index: CMakeLists.txt
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -77,8 +77,9 @@ if (CMAKE_SYSTEM_NAME MATCHES "OpenBSD")
   target_link_libraries(${PROJECT_NAME} "-lkvm")
 endif (CMAKE_SYSTEM_NAME MATCHES "OpenBSD")
 
-add_custom_command(OUTPUT lpass.1 DEPENDS ${CMAKE_SOURCE_DIR}/lpass.1.txt
+add_custom_command(TARGET ${PROJECT_NAME} PRE_BUILD DEPENDS ${CMAKE_SOURCE_DIR}/lpass.1.txt
         COMMAND a2x -D ./ --no-xmllint -f manpage ${CMAKE_SOURCE_DIR}/lpass.1.txt)
+install(FILES ${CMAKE_CURRENT_BINARY_DIR}/lpass.1 DESTINATION ${CMAKE_INSTALL_PREFIX}/man/man1)
 add_custom_command(OUTPUT lpass.1.html DEPENDS ${CMAKE_SOURCE_DIR}/lpass.1.txt
         COMMAND asciidoc -b html5 -a data-uri -a icons -a toc2 -o lpass.1.html ${CMAKE_SOURCE_DIR}/lpass.1.txt)