Support lib require in route file

[xuchaoying]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests is needed?
  • Tests for the changes have been added
• Docs is needed?
  • Docs have been added / updated

What kind of change does this PR introduce?

• Bug fix
• Feature
• Enhencement
• Refactor
• Documents
• Others

1. Support lib require in route file

const bodyParser = require('koa-bodyparser');

post('/XXXX').to.middleware(bodyParser).handle((ctx) => {
  console.log('ctx', ctx.request.body);
  ctx.type = 'html';
  ctx.body = ctx.request.body;
});

What is the related issue?

#157

Does this PR introduce a breaking change?

• breaking change？

Other information:

[codecov]

Codecov Report

Merging #178 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #178      +/-   ##
==========================================
+ Coverage   95.97%   95.98%   +0.01%     
==========================================
  Files          50       50              
  Lines        1688     1694       +6     
==========================================
+ Hits         1620     1626       +6     
  Misses         68       68              

Impacted Files	Coverage Δ
packages/svrx/lib/router/loader.js	100.00% <100.00%> (ø)
packages/svrx/lib/router/router.js	100.00% <100.00%> (ø)
packages/svrx/lib/svrx.js	95.28% <100.00%> (ø)

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[int64ago]

• Documents needed
• I prefer use instead of middleware

[int64ago]

middleware or handle ?

[xuchaoying]

• middleware

doc here： svrxjs/svrx-docs#41