add build script presets and stages

[myzhang1029]

v0.3 task:
e.g. in conf.toml:

[build]
preset="cmake" # or
preset="autoconf" # or
preset="buildsh" # (optional)
# or
[build.stages]
configure=[
'./autogen.sh',
'./configure',
]
make=[
'make'
]
install=[
'make install'
]
clean=[
'make distclean'
]

and the clean stage can be run automatically if build failed and debug is not set.
The old build.sh way will still work, and the buildsh preset says that explicitly.
The commands are run inside a shell (asyncio.create_subprocess_shell)
If any command failed, things won't continue.