Snabb lwAFTR version is Snabb version

Fixes snabbco#888.

src/core/main.lua

@@ -81,6 +81,7 @@ function select_program (args)
             usage(0)
          elseif opt == '-v' or opt == '--version' then
             version()
+            os.exit(0)
          else
             print("unrecognized option: "..opt)
             usage(1)
@@ -119,7 +120,6 @@ License: <https://www.apache.org/licenses/LICENSE-2.0>
 
 Snabb is open source software.  For more information on Snabb, see
 https://github.com/snabbco/snabb.]])
-   os.exit(0)
 end
 
 function programname (name)

src/program/lwaftr/lwaftr.lua

@@ -2,23 +2,15 @@ module(..., package.seeall)
 
 local lib = require("core.lib")
 
--- Retrieves latest version from CHANGELOG.md.
--- Format: ## [Version] - 2017-31-12.
 local function latest_version()
-   local filename = "program/lwaftr/doc/CHANGELOG.md"
-   local regex = "^## %[([^%]]+)%] %- (%d%d%d%d%-%d%d%-%d%d)"
-   for line in io.lines(filename) do
-      local version, date = line:match(regex)
-      if version and date then return version, date end
-   end
+   local v = require('core.version')
+   return v.version, v.extra_version
 end
 
 local function show_usage(exit_code)
    local content = require("program.lwaftr.README_inc")
-   local version, date = latest_version()
-   if version and date then
-      content = ("Version: %s (%s)\n\n"):format(version, date)..content
-   end
+   require('core.main').version()
+   print('')
    print(content)
    main.exit(exit_code)
 end