gitweb: Create Gitweb::Format module

gitweb: Create Gitweb::Format module

Create Gitweb::Format module in 'gitweb/lib/Gitweb/Format.pm'
to store the subroutines related to formatting of HTML
fragments required for gitweb.

This module depends on Config.pm, View.pm, Escape.pm,
Util.pm and Request.pm. It mainly contain functions returning
short HTML fragments or transforming HTML fragments. Also
include subroutines regarding avatar formatting.

Subroutines moved:
	format_log_line_html
	format_ref_marker
	format_subject_html
	picon_url
	gravatar_url
	git_get_avatar
	format_search_author
	format_author_html
	format_git_diff_header_line
	format_extended_diff_header_line
	format_diff_from_to_header
	format_diff_cc_simplified
	format_diff_line
	format_snapshot_links

Update 'gitweb/Makefile' to install Gitweb::Format alongside gitweb.

Signed-off-by: Pavan Kumar Sunkara <pavan.sss1991@gmail.com>