Merge bitcoin-core/secp256k1#1020: doc: remove use of <0xa0> "no break space"

812ff5c doc: remove use of 0xa0 "no break space" (fanquake)

Pull request description:

  This is miscellaneous, but I don't think these were being used on purpose?

ACKs for top commit:
  siv2r:
    ACK 812ff5c. The non-breaking space character is replaced with whitespace. Tested with [NBSP highlighter extension](https://marketplace.visualstudio.com/items?itemName=viktorzetterstrom.non-breaking-space-highlighter) on vscode.
  real-or-random:
    ACK 812ff5c

Tree-SHA512: ccfcc64798f5a5eb0c669eb00f4408ab713e6710d67fd15ee2a4dca0d052e27636d7f0ad312aa94be0cd068c7e7874441aa2e114c4118322d0c764398a4ff695

Author: real-or-random

configure.ac

@@ -160,7 +160,7 @@ AC_ARG_ENABLE(external_default_callbacks,
 AC_ARG_WITH([test-override-wide-multiply], [] ,[set_widemul=$withval], [set_widemul=auto])
 
 AC_ARG_WITH([asm], [AS_HELP_STRING([--with-asm=x86_64|arm|no|auto],
-[assembly optimizations to use (experimental: arm) [default=auto]])],[req_asm=$withval], [req_asm=auto])
+[assembly optimizations to use (experimental: arm) [default=auto]])],[req_asm=$withval], [req_asm=auto])
 
 AC_ARG_WITH([ecmult-window], [AS_HELP_STRING([--with-ecmult-window=SIZE|auto],
 [window size for ecmult precomputation for verification, specified as integer in range [2..24].]

include/secp256k1.h

@@ -264,7 +264,7 @@ SECP256K1_API void secp256k1_context_destroy(
  *  undefined.
  *
  *  When this function has not been called (or called with fn==NULL), then the
- *  default handler will be used. The library provides a default handler which
+ *  default handler will be used. The library provides a default handler which
  *  writes the message to stderr and calls abort. This default handler can be
  *  replaced at link time if the preprocessor macro
  *  USE_EXTERNAL_DEFAULT_CALLBACKS is defined, which is the case if the build