Configs with backslashes don't survive round-trip serialization.

[ClaytonHughes]

Version Information
From Nuget: Hocon and Hocon.Configuration 2.0.3

(Reproduced on dev, (482a9c1), with failing tests, here: ClaytonHughes@0e55a7c)

Describe the bug
When configurations are serialized, backslashes are not escaped. This means a round-trip serialization of a Config will not succeed.

To Reproduce
Steps to reproduce the behavior:

1. Have a backslash in your Config (e.g. by parsing a string with an escaped backslash)
2. Serialize it - note the output is incorrect (backslashes are not escaped)
3. Parse the serialization - note the tokenizer exception because of the invalid input

Expected behavior
Configurations serialize into valid Json/HOCON (backslashes are escaped).

Actual behavior
Configurations do not escape backslashes, producing (likely) invalid Json/Hocon.

Environment
net461, netcoreapp2.1