added some imports to test/Main.agda
added Makefile in test/
removed True from Prelude.Bool
Use if instead of pattern lambda in ShowBool
Changed Sigma to a data type.

Records are bad for compile-time performance!
Added some functions to Prelude.Sum

lefts, rights, partitionMap
Added ifYes to Decidable
README grammar
Added singleton and [_] to Prelude.List
Added isAlpha, isAlphaNum and isUpper to Prelude.Char
Added isNo to Prelude.Bool
Added Text.Lex
Merge branch 'master' into maint-2.4.0