Fix exception that occurs with libc++ regex engine

Fix exception that occurs with libc++ regex engine (#368)

The regex that parses header lines potentially causes an unlimited
amount of backtracking, which can cause an exception in the libc++ regex
engine.

The exception that occurs looks like this and is identical to the
message of the exception fixed in
https://github.com/yhirose/cpp-httplib/pull/280:

	libc++abi.dylib: terminating with uncaught exception of type
	std::__1::regex_error: The complexity of an attempted match
	against a regular expression exceeded a pre-set level.

This commit eliminates the problematic backtracking.

Deflate compression support when decompressing input body on Server

v0.5.6

Support for deflate compression (#360)

Fixed problems (#351 and #352)

#351
#352

Expect: 100-Continue support

v0.5.4

Fix #349

HEAD support for static file server

v0.5.3

Added a contributor to README

Proxy support and bug fixes

v0.5.2

Updated README

Added set_file_extension_and_mimetype_mapping server method and fixed problem with colon in URL

v0.5.1

Updated README

Better authentication support

v0.5.0

V0.5.0

set_interface support and fixed URL encoding problem when sending a request to proxy

v0.4.2

Code cleanup

Fixed build problem with Visual C++

v0.4.1

Fix #289: Fixed build problem with Visual C++