Add some tooling to build "preview" releases

They are available at: https://download.calibre-ebook.com/preview/
They will have version numbers with a patch level >= 100 so its
relatively easy for us to know when a bug report pertains to a preview
release.

setup/commands.py

@@ -18,7 +18,7 @@ __all__ = [
     'upload_to_server',
     'upload_installers',
     'upload_user_manual', 'upload_demo', 'reupload',
-    'stage1', 'stage2', 'stage3', 'stage4', 'stage5', 'publish', 'publish_betas',
+    'stage1', 'stage2', 'stage3', 'stage4', 'stage5', 'publish', 'publish_betas', 'publish_preview',
     'linux', 'linux64', 'linuxarm64', 'win', 'win64', 'osx', 'build_dep',
     'export_packages', 'hyphenation', 'liberation_fonts', 'stylelint', 'xwin',
 ]
@@ -81,7 +81,7 @@ recent_uas = RecentUAs()
 rapydscript = RapydScript()
 
 from setup.publish import Manual, TagRelease, Stage1, Stage2, \
-        Stage3, Stage4, Stage5, Publish, PublishBetas, ManPages
+        Stage3, Stage4, Stage5, Publish, PublishBetas, PublishPreview, ManPages
 manual = Manual()
 tag_release = TagRelease()
 stage1 = Stage1()
@@ -91,6 +91,7 @@ stage4 = Stage4()
 stage5 = Stage5()
 publish = Publish()
 publish_betas = PublishBetas()
+publish_preview = PublishPreview()
 man_pages = ManPages()
 
 from setup.upload import (UploadUserManual, UploadDemo, UploadInstallers,

setup/publish.py

@@ -126,6 +126,30 @@ class PublishBetas(Command):
         ).split())
 
 
+class PublishPreview(Command):
+
+    sub_commands = ['stage1', 'stage2', 'sdist']
+
+    def pre_sub_commands(self, opts):
+        version = tuple(map(int, __version__.split('.')))
+        if version[2] < 100:
+            raise SystemExit('Must set calibre version to have patch level greater than 100')
+        require_clean_git()
+        require_git_master()
+
+    def run(self, opts):
+        dist = self.a(self.j(self.d(self.SRC), 'dist'))
+        with open(os.path.join(dist, 'README.txt'), 'w') as f:
+            print('''\
+These are preview releases of changes to calibre since the last normal release.
+Preview releases are typically released every Friday, they serve as a way
+for users to test upcoming features/fixes in the next calibre release.
+''', file=f)
+        subprocess.check_call((
+            f'rsync -rh --info=progress2 --delete-after --delete {dist}/ download.calibre-ebook.com:/srv/download/preview/'
+        ).split())
+
+
 class Manual(Command):
 
     description = '''Build the User Manual '''

src/calibre/constants.py

@@ -5,7 +5,7 @@ from functools import lru_cache
 import sys, locale, codecs, os, collections, collections.abc
 
 __appname__   = 'calibre'
-numeric_version = (7, 6, 0)
+numeric_version = (7, 6, 100)
 __version__   = '.'.join(map(str, numeric_version))
 git_version   = None
 __author__    = "Kovid Goyal <kovid@kovidgoyal.net>"