* added doc for parameter 'coerce_float' in io.sql.read_frame
adjusted the indentation of doc of io.sql.read_frame
fixed conflict in sql.py
BLD: install pip serially
Merge pull request #4141 from cpcloud/travis-install-pip-serially

BLD: install pip serially
ENH melt uses column name if available
CLN test_reshape
DOC add release note about melt columns.name default behaviour
BLD: readd missing envar in ci/install.sh
BLD: add lxml back in
BUG: Make ExcelFile.parse pass kwds to TextParser
BUG: (GH4145/4146) Fixed bugs in multi-index selection with column multi-index and duplicates
Merge pull request #4139 from jtratner/excel_fix

BUG: Make ExcelFile.parse pass kwds to TextParser
Merge pull request #4148 from jreback/mi2

BUG: (GH4145/4146) Fixed bugs in multi-index selection with column multi index duplicates
TST: additional test case for GH4146
Merge pull request #4144 from hayd/melt_name

ENH melt uses column name if available
Merge pull request #4149 from jreback/mi2.2

TST: additional test case for GH4146
ENH col_level argument to melt
ENH MultiIndex columns with melt
ENH add drop_na argument to pivot_table