Bump dev version to 2.21.0. (#4656)

---
TYPE: NO_HISTORY
DESC: Bump dev version to 2.21.0.

Author: KiterLuc

tiledb/doxygen/source/conf.py

@@ -76,9 +76,9 @@
 author = 'TileDB, Inc.'
 
 # The short X.Y version.
-version = '2.20'
+version = '2.21'
 # The full version, including alpha/beta/rc tags.
-release = '2.20.0'
+release = '2.21.0'
 
 # Breathe extension configuration.
 doxygen_xml_dir = os.path.join(TILEDB_BUILD_DIR, 'xml/')

tiledb/sm/c_api/tiledb_version.h

@@ -27,5 +27,5 @@
  */
 
 #define TILEDB_VERSION_MAJOR 2
-#define TILEDB_VERSION_MINOR 20
+#define TILEDB_VERSION_MINOR 21
 #define TILEDB_VERSION_PATCH 0