Cache parsed properties, change provided properties to fields

[zanaptak]

Introduce longer cache for file and process parsed results in addition to the shorter generated type cache.

Also change the provided type to use public literal fields instead of properties. This improves the performance of large IDE completion lists.

Below are informal timings on large sets of Tailwind CSS classes, from the moment of typing a dot on the type until the unfiltered completion list appearing, also compared to a module of hard-coded literals. Time in seconds on a desktop i7-4790k CPU.

Source	Tailwind classes	Visual Studio 2019	Visual Studio Code
TypedCssClasses 0.3.1	13851	2.1	3.3
TypedCssClasses 0.4.0	13851	1.2	2.2
hard-coded module	13851	0.7	1.7
TypedCssClasses 0.3.1	5535	1.1	1.8
TypedCssClasses 0.4.0	5535	0.7	1.3
hard-coded module	5535	0.4	1.2

Note: The lower Tailwind class count obtained by configuring 1 responsive screen breakpoint instead of the default of 4. See Tailwind CSS theme configuration.

Fixes #7.