[Tolk] Embedded stdlib.tolk, CompilerState, strict includes

Several related changes:
- stdlib.tolk is embedded into a distribution (deb package or tolk-js),
  the user won't have to download it and store as a project file;
  it's an important step to maintain correct language versioning
- stdlib.tolk is auto-included, that's why all its functions are
  available out of the box
- strict includes: you can't use symbol `f` from another file
  unless you've #include'd this file
- drop all C++ global variables holding compilation state,
  merge them into a single struct CompilerState located at
  compiler-state.h; for instance, stdlib filename is also there

tolk/compiler-state.cpp

@@ -0,0 +1,47 @@
+/*
+    This file is part of TON Blockchain Library.
+
+    TON Blockchain Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 2 of the License, or
+    (at your option) any later version.
+
+    TON Blockchain Library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with TON Blockchain Library.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#include "compiler-state.h"
+
+namespace tolk {
+
+std::string tolk_version{"0.5.0"};
+
+CompilerState G; // the only mutable global variable in tolk internals
+
+void GlobalPragma::enable(SrcLocation loc) {
+  if (deprecated_from_v_) {
+    loc.show_warning(PSTRING() << "#pragma " << name_ <<
+                     " is deprecated since Tolk v" << deprecated_from_v_ <<
+                     ". Please, remove this line from your code.");
+    return;
+  }
+  if (!loc.get_src_file()->is_entrypoint_file()) {
+    // todo generally it's not true; rework pragmas completely
+    loc.show_warning(PSTRING() << "#pragma " << name_ <<
+                     " should be used in the main file only.");
+  }
+
+  enabled_ = true;
+}
+
+void GlobalPragma::always_on_and_deprecated(const char *deprecated_from_v) {
+  deprecated_from_v_ = deprecated_from_v;
+  enabled_ = true;
+}
+
+
+} // namespace tolk