Command Line Parsing

- Implemented Arguments::extract_command to locate the command
  keyword in an argument list.
- Implemented Arguments::extract_sequence to locate and remove an ID
  sequence from an argument list.
- Added unit test for extract_sequence.
- Stubbed all Argument::extract_<object> methods.
- Simplified code in (soon to be obsolete) Sequence.cpp.

test/.gitignore

@@ -1,6 +1,7 @@
 *.o
 *.data
 *.log
+arguments.t
 att.t
 autocomplete.t
 cmd.t