all: assorted cleanups and updates

Changes include:
  - add a bunch of "noexcept", mostly to operators and forceinline
  - use "uchar"
  - use "charptr"
  - rename options_t to Options
  - add ptr_check_no_overlap()
  - rewrite p_exe.cpp, NFCI
  - clang-format help.cpp
  - spelling fixes

src/compress/compress.cpp

@@ -78,7 +78,7 @@ int upx_compress(const upx_bytep src, unsigned src_len, upx_bytep dst, unsigned
     // force users to provide *dst_len
     assert(*dst_len != 0);
 #endif
-    // for UPX, we always require a reasonably sized outbut buffer
+    // for UPX, we always require a reasonably sized output buffer
     assert(*dst_len >= MemBuffer::getSizeForCompression(src_len));
 
     if (!cresult)