Some unicode control characters are incorrectly formatted

[michael-mwp]

Issue created from fantomas-ui

Some unicode control characters are incorrectly formatted resulting in uncompilable code.
Issue identified with the backspace and formfeed characters.

This bug has been introduced in v3.0.0

Code

namespace SomeNamespace

module SomeModule =
    let backspace = '\b'
    let formFeed = '\f'

Error

namespace SomeNamespace

module SomeModule =
    let backspace = '�'
    let formFeed = ''

Options

Fantomas 3.0.0-10/11/2019

Name	Value
IndentOnTryWith	false
IndentSpaceNum	4
KeepNewlineAfter	false
PageWidth	120
ReorderOpenDeclaration	false
SemicolonAtEndOfLine	false
SpaceAfterComma	true
SpaceAfterSemicolon	true
SpaceAroundDelimiter	true
SpaceBeforeArgument	true
SpaceBeforeColon	false
StrictMode	false