Add checks variable modifiers

[Stef-00012]

For numbers:

• >X: Greater than X ¹
• >=X: Greater or equal to X ¹
• =X: Equal to X ¹
• <=X: Lesser or equal to X ¹
• <X: less than X ¹

For strings:

• =Y: Equals to Y ²
• ~Y: Contains/Includes Y ²
• $Y: Starts with Y ²
• ^Y: Ends with Y ²
• exists: If the string is not null or empty ""

For booleans:
istrue: Is true

they work like so
{type.prop::mod["true string"||"false string"]}

Example:
{file.maxViews::>0["{file.views}/{file.maxViews}"||""]}
This will return

• <views>/<max_views> (eg. 2/7) when maxViews is greater than 0
• Nothing when it's 0, less than 0 or null

Footnotes

1. X is any number ↩ ↩² ↩³ ↩⁴ ↩⁵

2. Y is any string ↩ ↩² ↩³ ↩⁴