Refactoring eval Tests
BugFix
Refactoring Syntax Test
Remove redundant context information
Added `isVal` case (free var)
Remove redundant context when evaluate term
Added Test case "when undefined function found while evaluate the term"
Added foundation specs for Terminate type
Refactoring Chapter7 construction
Added foundation specs for free variable of term type
Merge branch 'Chapter7'

* Chapter7:
  Added foundation specs for free variable of term type
  Refactoring Chapter7 construction
  Added foundation specs for Terminate type
  Added Test case "when undefined function found while evaluate the term"
  Remove redundant context when evaluate term
  Added `isVal` case (free var)
  Remove redundant context information
  Refactoring Syntax Test
  BugFix
  Refactoring eval Tests