Fix #84 by improving functions that enforce snake_case and kebab-case for special cases

Author: plokhotnyuk

macros/src/main/scala/com/github/plokhotnyuk/jsoniter_scala/macros/JsonCodecMaker.scala

@@ -77,7 +77,7 @@ object JsonCodecMaker {
         sb.append(ch)
         true
       } else {
-        if (isPrecedingLowerCased) sb.append('_')
+        if (isPrecedingLowerCased || i < len && isLowerCase(s.charAt(i))) sb.append('_')
         sb.append(toLowerCase(ch))
         false
       }
@@ -100,7 +100,7 @@ object JsonCodecMaker {
         sb.append(ch)
         true
       } else {
-        if (isPrecedingLowerCased) sb.append('-')
+        if (isPrecedingLowerCased || i < len && isLowerCase(s.charAt(i))) sb.append('-')
         sb.append(toLowerCase(ch))
         false
       }

macros/src/test/scala/com/github/plokhotnyuk/jsoniter_scala/macros/JsonCodecMakerSpec.scala

@@ -1083,7 +1083,7 @@ class JsonCodecMakerSpec extends WordSpec with Matchers {
     "transform snake_case names to camelCase" in {
       JsonCodecMaker.enforceCamelCase("o_o") shouldBe "oO"
       JsonCodecMaker.enforceCamelCase("o_ooo_") shouldBe "oOoo"
-      JsonCodecMaker.enforceCamelCase("O_OOO_111") shouldBe "oOoo111"
+      JsonCodecMaker.enforceCamelCase("OO_OOO_111") shouldBe "ooOoo111"
     }
     "transform kebab-case names to camelCase" in {
       JsonCodecMaker.enforceCamelCase("o-o") shouldBe "oO"
@@ -1100,7 +1100,7 @@ class JsonCodecMakerSpec extends WordSpec with Matchers {
     "transform camelCase names to snake_case" in {
       JsonCodecMaker.enforce_snake_case("oO") shouldBe "o_o"
       JsonCodecMaker.enforce_snake_case("oOoo") shouldBe "o_ooo"
-      JsonCodecMaker.enforce_snake_case("oOoo111") shouldBe "o_ooo_111"
+      JsonCodecMaker.enforce_snake_case("OOOoo111") shouldBe "oo_ooo_111"
     }
     "transform kebab-case names to snake_case" in {
       JsonCodecMaker.enforce_snake_case("o-O") shouldBe "o_o"
@@ -1117,7 +1117,7 @@ class JsonCodecMakerSpec extends WordSpec with Matchers {
     "transform camelCase names to kebab-case" in {
       JsonCodecMaker.`enforce-kebab-case`("oO") shouldBe "o-o"
       JsonCodecMaker.`enforce-kebab-case`("oOoo") shouldBe "o-ooo"
-      JsonCodecMaker.`enforce-kebab-case`("oOoo111") shouldBe "o-ooo-111"
+      JsonCodecMaker.`enforce-kebab-case`("OOOoo111") shouldBe "oo-ooo-111"
     }
     "transform snake_case names to kebab-case" in {
       JsonCodecMaker.`enforce-kebab-case`("o_O") shouldBe "o-o"