Wrap results of the Reader in MaybeError to indicate errors
Change Lexer to return a list of tokens wrapped in MaybeError.

Lexer interface is changed so that only one static method is exposed.
Remove unneeded space
Lexer.readTokens now returns Iterator instead of List
Implement error reporting and recovering in Reader
Fix error recovery set for Term
Add program for checking syntax
Improve error recovery for maps
Implement Toke.toString()
Add helper methods for creating sets of TokenTypes
Split parsers for simple expressions and expressions that may introduce a block
Lexer: Close a logical line even if braces was not closed
Add method checkAndRead to simplify parser
Do error recovery even in case of lexical errors
Rename LINEEND to LINE_END
Implement checking according to schema in Checker