Added support for more unquoted characters and inline empty blocks

[lasa01]

CSGO has material (.vmt) files that have unquoted keys starting with $.

For example, csgo/materials/grass/hr_grass/grass_a.vmt:

LightmappedGeneric
{
$baseTexture "grass/hr_grass/grass_a"
$bumpmap "grass/hr_grass/grass_a_normals"

}

This fixes the parsing of these files.

[rossengeorgiev]

This PR will certainly resolve that specific case, but its probably best to add $ as part of the character class. We also need unit tests for this.

[lasa01]

Moved the changes to the character set and updated the weird unquoted character test case.

Also extended support for other missing characters in unquoted keys and values:

• % in keys (e.g. csgo\materials\detail\detailsprites_overgrown_massive9.vmt)
• single / in values (comments still work) (e.g. csgo\materials\liquids\canalswater_cheap.vmt)
• $ in values (e.g. csgo\materials\models\error\new light1.vmt)
• < > in keys and values (e.g. csgo\materials\particle\fire_burning_character\fire_molotov.vmt, csgo\materials\trash\hr_t\hr_trash_a.vmt)

Also added support for inline empty blocks directly after keys, and a corresponding test case, e.g.:

		"Proxies"
		{
			"EntityOrigin" {}
		}

(csgo\materials\models\player\custom_player\econ\head\ctm_fbi\ctm_fbi_v2_head_varianta.vmt)

[rossengeorgiev]

This looks really good. Happy to merge after the comments are addressed.

It would be interesting to see how much of these testcases are covered: https://github.com/SteamDatabase/ValveKeyValue/tree/master/ValveKeyValue/ValveKeyValue.Test/Test%20Data/Text