exceptions: pretty diagnostics

[xnacly]

This pr adds pretty printing for exceptions::SyntaxViolation and wraps the main with an entry_point function to catch all exceptions::Exception and pass them to print_exception at a single point.

Progress:

• Exceptions
  • SyntaxViolation
  • StackTrace
• Lexer
  • UnexpectedEof
  • InvalidCharacterInHexEscape
  • UnexpectedCharacter
  • BadEscapeCharacter
  • ReadError
• Parser
  • UnexpectedEof
  • ExpectedClosingParen
  • UnexpectedClosingParen
  • InvalidPeriodLocation
  • NonByte
  • UnclosedParen
  • CharTryFrom
  • Lex
  • ParseNumberError
  • UnexpectedToken

These changes result in the following output for a list of faulty inputs:

Uncaught exception:
 - Message: undefined variable

--> fact.scm:8:1:
007 |        (iter b (+ a b) (- count 1))))
008 |  (ite 0 1 n))
    |  ~ here

> i
Uncaught exception:
 - Message: undefined variable

--> <prompt>:1:0:
001 | i
    | ~ here

Uncaught exception:
 - Message: No such file or directory (os error 2)
 - Condition: #<&assertion>
 - Condition: #<&i/o>