added alter table command to fluent query builder (progress)

include/matador/sql/dialect.hpp

@@ -143,6 +143,7 @@ private:
     {dialect_token::Drop,        "DROP"},
     {dialect_token::Remove,      "DELETE"},
     {dialect_token::Insert,      "INSERT"},
+    {dialect_token::Alter,       "ALTER"},
     {dialect_token::Table,       "TABLE"},
     {dialect_token::Into,        "INTO"},
     {dialect_token::Values,      "VALUES"},
@@ -172,6 +173,9 @@ private:
     {dialect_token::Set,         "SET"},
     {dialect_token::NotNull,    "NOT NULL"},
     {dialect_token::PrimaryKey, "PRIMARY KEY"},
+    {dialect_token::ForeignKey, "FOREIGN KEY"},
+    {dialect_token::AddConstraint,  "Add CONSTRAINT"},
+    {dialect_token::DropConstraint, "DROP CONSTRAINT"},
     {dialect_token::Begin,       "BEGIN TRANSACTION"},
     {dialect_token::Commit,      "COMMIT TRANSACTION"},
     {dialect_token::Rollback,    "ROLLBACK TRANSACTION"},