Added pg::proof_graph_t::enumerate_edges_to_observation.
Small changes.
Revised definitions of some classes. (halfway)
Updated various things.

Added function to omit invalid candidate for chaining.
Changed the design about mutual exclusive nodes.
Added some methods and fields for mutual exclusive edges.
Renamed list_for_map into comparable_list.
etc...
Revised the process to create reachable-matrix for acceleration. (halfway)
Revised the process to create reachable-matrix for acceleration.
Added function to omit invalid unifications.
Added function to exclude functional predicates in creation of reachable matrix.
Revised functions to output.
Updated various things.(halfway)

Updated the toy problem.
Revised procedures in lhs::basic_lhs_enumerator_t for acceralation.
Revised definitions of some methods of pg::proof_graph_t.
Changed the operator "_|_" to "xor".
Implemented the function to check mutual exclusiveness on chaining. (halfway)
Fixed some bugs.
Added the function to check literals' overlap on chaining.
Updated README.md
Added the function to use reachable-matrix on creation of LHS. (halfway)
Added the function to normalize file pathes.
Implemented the function to use reachable-matrix on creation of LHS.

Revised the procedure to set distance-provider to knowledge-base.
Added a function of node_t for providing its evidences.
Debugged changes in last updates.
Added a constraint for unification, which prohibit unification between a node and its ancestor.
Implemented costed_converter_t. (halfway)
Added option DISABLE_CUTTING_LHS.