Ignored warnings for unused classes (#383)

# ical4j: keep all iCalendar properties/parameters (used via reflection)

-keep class net.fortuna.ical4j.** { *; }

# we are not using those optional features of ical4j

-dontwarn org.jparsec.** # parser for filter expressions

-dontwarn javax.cache.** # timezone caching

# we use enum classes (https://www.guardsquare.com/en/products/proguard/manual/examples#enumerations)

-keepclassmembers,allowoptimization enum * {

    public static **[] values();

-dontwarn org.joda.**

-dontwarn org.json.*

-dontwarn org.xmlpull.**

# Seems to be incorrectly detected in https://github.com/ical4j/ical4j/blob/176fc84a4785d6f87be5dd18a20c6f83c6287b35/src/main/java/net/fortuna/ical4j/validate/schema/JsonSchemaValidator.java#L36C1-L36C39

# Should be fixed eventually by ical4j

# Commented in https://github.com/ical4j/ical4j/blob/176fc84a4785d6f87be5dd18a20c6f83c6287b35/build.gradle#L76

-dontwarn com.github.erosb.jsonsKema.*