turkish: Remove proper noun suffixes

In modern Turkish orthography, an apostrophe is used to separate proper
names from any suffixes, so before we do anything else we now truncate
at the first apostrophe.

Fixes #188

algorithms/turkish.sbl

@@ -1,7 +1,6 @@
 /* Stemmer for Turkish
  * author: Evren (Kapusuz) Çilden
  * email: evren.kapusuz at gmail.com
- * version: 1.0 (15.01.2007)
  *
  * stems nominal verb suffixes
  * stems nominal inflections
@@ -69,6 +68,8 @@ routines (
   post_process_last_consonants
   postlude
 
+  remove_proper_noun_suffix
+
   stem_nominal_verb_suffixes
   stem_noun_suffixes
   stem_suffix_chain_before_ki
@@ -439,6 +440,14 @@ backwardmode (
   )
 )
 
+define remove_proper_noun_suffix as (
+  // https://en.wikipedia.org/wiki/Turkish_language says "In modern
+  // Turkish orthography, an apostrophe is used to separate proper names
+  // from any suffixes" with the example "Türkiye'dir ("it is Turkey")".
+  // Therefore we truncate at the first apostrophe.
+  do (goto '{'}' [ tolimit ] delete)
+)
+
 // Test if there is more than one syllable.
 // In Turkish each vowel indicates a distinct syllable.
 define more_than_one_syllable_word as (
@@ -454,6 +463,8 @@ define postlude as (
 )
 
 define stem as (
+  do remove_proper_noun_suffix
+
   more_than_one_syllable_word
 
   backwards (