Added map parsers

tribune-core/src/main/kotlin/com/sksamuel/tribune/core/maps/maps.kt

@@ -0,0 +1,17 @@
+package com.sksamuel.tribune.core.maps
+
+import arrow.core.sequence
+import com.sksamuel.tribune.core.Parser
+import com.sksamuel.tribune.core.flatMap
+
+fun <I, K, V, R, E> Parser<I, Map<K, V>, E>.parseKeys(parser: Parser<K, R, E>): Parser<I, Map<R, V>, E> {
+   return this.flatMap { input ->
+      input.map { (key, value) -> parser.parse(key).map { Pair(it, value) } }.sequence().map { it.toMap() }
+   }
+}
+
+fun <I, K, V, R, E> Parser<I, Map<K, V>, E>.parseValues(parser: Parser<V, R, E>): Parser<I, Map<K, R>, E> {
+   return this.flatMap { input ->
+      input.map { (key, value) -> parser.parse(value).map { Pair(key, it) } }.sequence().map { it.toMap() }
+   }
+}